My puppy has dry heaves and yellow diarrhea what could it be?

Gryffindor is eight weeks old shows no sings of lethargy, I don't know if he's eating and drinking because i just got him this mourning. He's had his first puppy shot. He has dry heaves and yellow diarrhea(which doesn't really smell bad and isn't bloody at all). I'm wondering if this is a simple parasite or what else could possibly cause it. I'm already attached to him and would hat it if something were to happen.