My puppy has been acting odd all day and his stomach is making loud noises, what's wrong?

All day he has been sluggish and is refusing to eat. I've tried feeding him a lot of things- even his favorite treats. He's turning down everything. All he wants to do is sleep. He's thrown up once today and it had grass in it. What's wrong with him and should I go ahead and take him to the vet tomorrow morning?