My cat is losing hair

Hi so I've been struggling with my foster cat. He's been having, what I suspect, food allergies. He's being having legions on his skin that become bloody. I took him to the vet and got him lots of blood tests, ringworm test, etc. etc. but it all came out negative. I used to feed him fish, beef, and chicken.

My foster coordinator told me to not feed him fish and then I just gave him chicken. He got a lot worse so I put him on a novel diet of lamb and turkey. He had issues with the turkey as well so I suspect he doesn't like feathered things. The vet gave him steroids but he got sick after that.

So I thought I would just give him lamb. That worked for 2 weeks and he got a lot better! Everything was going just fine, then he stopped eating. He got tired of it. I know because I gave him beef and lamb and now he's eating. The problem is now he's having hair loss.

This is incredibly frustrating because I don't know whether his hair loss is because of the beef or if it's lingering from the other stuff he had long ago. He's not scratching it so it's not itchy. The vets are worthless. I just saw the vet a week ago and they didn't know what was going on. I feel like I'm alone and this is the first time I've had a cat so I don't know what to do.

Anyone have suggestions on what to do? I want to try rabbit and lamb instead. Obviously I want to just get him on lamb, but I need help on how to get him to eat it when he gets bored. I can't imagine him going 12 weeks with just one food.

Chicken, beef, and fish are pretty high on foods that cause allergies. You're right on track with trying lamb, which is a more novel protein. Other good options are as you mentioned rabbit, and venison, and maybe even pork. Boredom can be an issue with restricted diets so you could try and find some toppers or freeze dried meat treats that might help entice him to eat. I know Orijen makes some lamb ones as well as some that have venison too. If you can find 2 or 3 proteins he can tolerate that should be enough variety. 

Hi thank you for replying. 

I've put him on Lamb and Rabbit for now. Let's see how it goes. I'll try putting some treats in his meal when he gets bored.