I'm sorry to hear this. Hopefully your vet will be able to diagnose him properly. Many times if a cat is having vomiting or diarrhea issues vets will just call it IBD, put them on pred, and that's it.

My oldest cat Storm was also having vomiting issues and finally after doing a more specific blood test he was diagnosed with having small intestinal disease. He also had low folate so he's being supplemented with folic acid for 6 weeks and hopefully his intestine will start working properly after this. He's also on pred and pepcid at night. My vet and I are hoping that we'll eventually be able to wean him down to a very low doseage of pred but he still may need to take 5mg of pepcid at night.

Lots of prayers and positive thoughts are being sent his way. Please continue to keep us updated about him.