My cat has suddenly lost over 2 pounds - please help

I am going to try and post this on as many forums and email it to as many people as possible. I am desperate for answers. The cat whom I love more than anyone/anything is not doing well and I want to save him.
About 3 months ago Nate, my eight and a half year old male neutered cat, began to lose weight. Within the last few weeks this weight loss became very noticable(before I thought I was just paranoid). A trip to the vet revealed that he has lost a little over 2 pounds(since November). We just haven't found out why. Here's what we do know:
- In November I brought him to his neurologist because he was exibiting some head shaking and scratching at his right ear. He said his ears were relatively clean and prescribed an ear wash which I was reluctant to use(fear of safety, I'm a bit of an "it must be natural!" nut).
- He has seen a neurologist because, over 2 years ago, he had a neurological episode that resembled a vascular stroke - cause still unknown. His right limbs were paralyzed but he has recovered well with only a little weakness left, mostly in his front leg. At the time, he was on prednisone(yes, it's scary drug but so was the "stroke") and antibiotics - which might not have helped at all.. we'll never know. He hasn't been on any medications or had any other neurological episodes since.
- About 2 weeks ago I brought him to a nearby vet and had bloodwork ran. Everything came back normal with the exception of low potassium levels(no vet has seen this as a concern) and a thyroid test that I believe was 2.8(I was told it was in the normal range but we rechecked it anyway and it came out normal again). His potassium levels were low in his November 2005 bloodwork and I have read that this can be an early indicator of kidney problems but I also know that prednisone can lower potassium levels.
- He was supposed to have a fecal(done on second visit.. no parasites) and a urinalysis at the time but they could not get either from him. For some reason, on a subsequent visit for an abdominal ultrasound, they still did not collect urine from him. I haven't noticed him urinating or drinking more frequently until tonight when he seemed to be drinking more than usual. We were running the heat pretty high and he had had dry treats and sardines earlier so that might have been why, though. The abdominal ultrasound showed nothing abnormal with the exception of some "debris" in the bladder, which my current vet does not see as a concern(though he wants me to get him in for the urinalysis-at the original clinic-, of course.)
- When I brought him to the original vet I made the mistake of agreeing to a Rabies vaccination(who vaccinates a sick cat.. or any indoor cat for that matter? I know.. I made a stupid mistake, as did the vet) and a dewormer(again, stupid. I know better). He went downhill quickly that night, appearing very weak when he had seemed relatively normal(aside from the weight loss) before. I rushed him to the emergency room in tears, they checked his vitals, and he began to recover the next day.
- He had a chest and abdominal(I believe) xray and everything looked fine.
- He had an echocardiogram and everything looked fine.
- He saw an internal medicine specialist and she was stumped.
- He had been on Wellness(mostly wet, mostly the chicken formula) exclusively for almost 2 years. In October, however, we switched one of our cats over to a Limited Ingredient Rabbit & Pea formula to rule out food allergies. The other cats(I have 4 total) were still getting Wellness at first, then it was just Rabbit & Pea for everyone until the 2 pounds of weightloss was confirmed. Now everyone is on Wellness again with occasional treats like Greenies, chicken babyfood, tonight's sardines(canned in spring water, no salt added, with bones), and a bite now and then of "people food"(My boyfriend and I are vegans so this means vegetarian foods of course.) With the exception of the evening of the Rabies Vaccination, Nate has been eating with the same enthusiasm as before for the most part, though very recently I believe there might have been a decline.
- He has become less active than he was before. At times he seems lethargic but other times he'll play a bit or explore the house.
- He seems down and just.. not feeling right.
- He might be seeking out heat moreso than usual. Our house can get pretty cold(we live in Occidental) and he's grown very attached to the blazing heat of the wall heater.
- He doesn't appear to be defecating or urinating more than usual but I work fulltime and am gone about 13 hours of the day(long commute, sharing a car) and three other cats are using the boxes. Tonight I did notice that he got in the box, scraped around, did nothing, and got out and then repeated this a few minutes later but it was right after I cleaned the box and his siblings began to use it so I don't know if it's a concern or not. I don't think he was actually trying to urinate or deficate.
- He seems hydrated, no vomiting, no loose stool that I have noticed, no fever, no high blood pressure, no low blood pressure, no rapid heartbeat, no noticable swellings, no coughing even(he was coughing when I brought him to the first vet but he has always had a seasonal cough around this time of year and it's been dismissed as allergies..), no sneezing, no discharges of any kind. He seems healthy aside from the dramatic weight loss and decreased energy/mood.
- He is a completely indoor cat though he slipped out and became lost for a few days about 3 years ago. When I got him(over 8.5 years ago) he was a young feral kitten.
He's seen a total of 4 different vets, an internal medicine specialist, and a cardiologist. We live in Occidental so we started with the Forestville Animal Hospital(he saw one doctor there, another was present for his abdominal ultrasound, and one saw him at Animal Care Center in Rohnert Park the night I brought him in after the Rabies vac. reaction - she just transfered to the Forestville clinic from ACC). He then saw the other two doctors at ACC and the last doctor he saw was at the Central Animal Hospital(?) in Petaluma(his ACC neurologist refered us to him). The latter vet has suggested waiting a month to see if switching back to Wellness puts some weight back on him. The next step, after the urinalysis of course(I am very upset that this has not been performed. I think they simply forgot on his last visit to the Forestville clinic), would be a CT scan to look for tumors that the ultrasound might have missed. I am willing to pay anything to save Nate but I fear that I will exhaust all of my funds trying to figure out what is wrong with him only to not have any money left to treat him. I have maxed out all of my credit cards(I am still in quite a bit of debt from the neurological episode and a short period of unemployment) and spent my rent money. In otherwords, we are almost completely broke. I have asked everyone I know(which means a few people) for money but no one is able to help. I can and will try applying for more credit cards and of course saving every penny I make(I make $10 an hr so yeah it's not a lot) but I'm told a CT scan will be over $1000.
So I'm looking for suggestions of places to bring him for further testing/more opinions. Perhaps a place where I can make payments or even do a work exchange(I have some experience from volunteering at an animal shelter, pet sitting, and just living with animals all my life.). I'm mostly, however, looking for answers. What could this be? Have you heard of something like this before? Diabetes is ruled out, he doesn't seem to be urinating enough for it to be a kidney issue, it doesn't seem to be neurological, his thyroid was rechecked in a more thorough test but the vet suggested that we recheck again in a month as it(hypertyroidism) could show up then, he has no known parasites so far, and he might have put on a little bit of weight within the last few days(hard to tell, we're trying to get a hold of a baby scale.) Any ideas here? Any questions?
ANY advice would be greatly appreciated. This is my son here and I love him very much. He's a wonderful, very special, and incredibly sweet cat and he deserves the best of care.
Thank you to anyone who reads this.

Sorry you and your furbaby are having to go through this.

My only thoughts are -- (1) get that urinalysis done ASAP. Especially with the scratching around in the litterbox w/o doing anything, I'd be very concerned about getting it done sooner than soon.
(2) Find one vet that you completely trust who can look over all these results and coordinate his care. Having so many vets and apparently no one vet really spearheading his care worries me that something obvious might be getting overlooked, and that there is no concrete plan of care. Having one vet say "let's try this" and another one saying "let's try this (completely different approach)" makes it difficult to narrow anything down, not to mention how stressful and confusing I'm sure it is for you. Or --
(3) Ideally, if you are anywhere near a university vet school, I'd recommend taking him there if at all possible. They are set up to deal with the puzzling cases, and have specialists who are used to working as a team.
Good luck!

I completely agree with what Snuffles said!
In your shoes I think I would ask for x-rays again, full head and thoracic.
Are his lymph nodes swollen?

Maybe he is constipated, if you have multiple cats it is hard to tell which one has gone and which one hasn't.
I would think it is that or a UTI, or renal problems.
Have your Vet prescribe an appetite stimulant for your cat.

Has his mouth-teeth/gums been checked really well for ulcers, loose teeth, infection etc. etc.

Has his blood glucose been checked??I would request when you get urine to send it off to a diagnostic laboratory that way they can check it a little more in depth. I would also recommend running a Rabies titer to see what his immunity level is at, since you were concerned about the vaccination possibly being a culprit. Best of luck to you that you find an answer soon...

you say he got out somewhere around 3 years ago. has he been tested for felv/fiv, recently since his out episode. also he really needs a thorough urine examine, to rule out stones or crystals.

what about IBD, arthritis- not moving= less muscle mass= weight loss, or hypokalemia. Did you post on craigs list a few days ago? My cat has gone through the same thing as yours so far. He is 14 and has lost about 2 pounds, had multiple x-rays done, 8 doctors, abdominal ultrasound, blood, blood to msu, urinalysis, on prednisolone for possible ibd, slightly low potassium.
here is an article I found regarding CRF (which your cat does not have) and hypokalemia. It gives you an idea of symptoms

im probably too late on this , but my 17 yr old normally 6lb cat lost about 1 1/2 lbs within 2 months which is a lot. she was diagnosed with hyper thyroid-
i dont know a heck of a lot about it but basicly thier thyroid is working too fast & they are not absorbing all the nutrients from thier food therefore eating more, yet losing wieght.
we have to give her a pill once a day and she is fine now (the pills are for life but they are only $20 a bottle)

she had a t4 done already with normal results.

oops i didnt read her whole post