Have you recently changed his cat food? My neighbor has a male cat that vomits any cat food except one that the vet sells her to give him. That particular cat food is for cats with intestinal problems. I don't know if this might help also, but I recently had a 3 month old kitten with vomiting issues as well. I took her to the vet also and she checked out fine. They only thing they thought she might have was a viral infection which she might had contracted at the shelter where she was. I was adviced by a breeder to try plain yogurt. yogurt helps kill the bad bacteria in the intestine. It helped my kitten tremendously and she also said to give her pedialyte if she wasn't drinking water. I think this helped save my kittens life. They can very easily become dehydrated. I was adviced if she didn't want to eat at all to force feed the yogur which I did a few days only and in a short time she was eating more and more on her own mixed with a little cat food. If I were you, I'd try that
