How old is the pup?
Was the stool dark or have blood in it with a foul odor?
Has the puppy been lethargic meaning not playing around just laying around?
Have you tried giving the dog some pedialyte none flavor kind?
If you haven't tried the last question atleast try to get some fluids in the pup cause it could dehydrate. You should really take it to the vet but itf you can get it to hold down some fluids it may can wait until morning but would be better if seen today. Unfortunately your looking at a pricey emergency office visit today.
This happened to my boy over the summer and I panicked and ran to the vet and it was probably unnecessary. But depending on your pups age being over careful is never a bad thing. My boy was 16 weeks old at the time. If it happened now, I would try this before going to the vet
Is there blood in the stool? If no, more then likely he at something he shouldn't have. As MSK said, try pedalyte. Get him to drink. Go get some chicken breasts(boneless) boil it and give it to him with brown rice. Do that for a few days until his stools are normal.
When my pup threw up, I found a shoe lace and broken water balloon pieces....most likely that's what the problem was
Try some chicken broth or beef broth. As long as they are going the bathroom there isn't a blockage (not being able to hold anything down is concerning) hopefully you can call your regular vet tomorrow if thy continue to not eat and act lethargic.