feral cat is losing weight

About a year ago a women living in my apts. got a cat from a farm, he wouldn't stay inside so she left him when she moved. I have been taking care of him. He was sick last year so I took him to the vet, he had a serious respiratory infection, my indoor cat also got sick, it ended up costing me about $800 but they both recovered after 2 rounds of treatment.He will not stay inside or use a litter box. He got very fat over the winter but has lost a lot of weight very quickly., he doesn't look well. He was tested for leukemia and was okay. He has had all vaccinations. I'm living on disability and still paying off the $800 from the last visit. Any help would be greatly appreciated. I should add that I feed many stray cats so maybe he picked up something. Thanks for any advice you can offer.

He most likely has parasites, but he might also have a thyroid condition and/or diabetes.  If possible, get him a vet for a check up and a blood test.  You might look at some of the links posted for help with affordable vet care at the top of the forum's main page as well.

That was I was thinking it might be. I'll call the vet tomorrow, he should give me a discount since I take every stray to him.Lol  Thank you for replying.