Has he had all of his vaccines?You need to keep him hydrated.You could try and see if maybe he would eat some rice and chicken broth.I would let your vet check him as soon as possible.At that age it is hard to say what the problem could be.Has he been Dewormed?
You need to see a vet! He is probably dehydrated and needs fluids. There are many things that can cause him to be sick, parvo being one of them.