If you have some Nutri-Cal, I'd give him some of that for now. He probably is sick from the teeth. I'm guessing here. Kacee got sick when she was teething and she had a really bad time of it. I never had one so sick before while they were teething. If I were you, though, I think I'd hit the vet's office first thing in the morning. Could be more going on there. Hope you're doing ok.
I almost forgot. If you have a syringe or dropper, try giving him some water that way.