Skinny cat that throws up.

Current AGE: 8-9 years old

Stray found: around 7-8 months

He was sick when I found him.  Vetted him in all ways.  Had a throw up problem since I found him.  I tried all different foods to find one that he wouldn't throw up but figured out it was probably how fast or how much he would eat.  Multiple x-rays and blood work finds no problems.  Fast forward, 4 years ago or so my vet put him on royal canin veterinary gastro intestinal high energy dry food.  It helped his throw up abut 50% which was good.  He was still skinny but his weight was stabilized at 6 lbs (5-6 year old).  I moved and took him into another vet and he was pre kidney disease.  So I had to put him on can food.  He is a picky eater and can is not his favorite.  I tried the same food but in can and he had no interest.  I've tried many until I found one by natural instinct. He had can food (a lot of throw up days) for a year.  He was tested and no longer pre-kidney.  during the following year I went out of town and had to leave dry food, Natural Instinct raw.   I took him again with a mixture of more dry then wet and again his numbers looked good.  His weight is around 7 lbs, almost exact same weight has the year before.  Hope that's enough history

He is sooo skinny, just unhealthy looking.  Sometimes his fur looks separated and oily but his blood work came out fine for what ever they typically test for on his yearly check up. (believe in preventative medicine)  I only can feed him a teaspoon of wet food at a time otherwise when I put more he throws up.  I leave dry out all the time so he can nibble all day.

Is there anything else I can feed him (picky eater) that might add weight to him?

Or has anyone had similar problems and found a cure for throwing up or weight gain.

thank you

If he is eating something (dry or hard) and not throwing up and still not gaining weight then something is up. If he throws up most things then this is more than likely what the weight issue is. My old IBD guy used to throw up all of the time and the only thing that stopped it was getting Cerenia injections every few days, the pills did nothing for him. When my guy had a low appetite I would feed him anything he would eat and pretty much as much as he wanted but not all at once. Try some fancy Feast which is like cat crack just to get him eating and then try switching back and forth with that and what he should be eating. I went to the store and bought a few of everything and then just tried each one to see if he would eat it and how long it stayed down. For my guy once he was on the Cerenia he could eat and he wasn't throwing up so it may be worth a short trial. There are a lot of things that can make them lose a lot of weight and you won't always find it on the standard blood test. I would also test his B12 levels which again is a different test and see how those stand. How is his hydration? Are his gums nice and pink and is there a little moisture in his cheek pouch?