Ahh, poor baby. Little pups can have digestive issues. Did you recently bring him home? They get really used to one food and if you change it at all, they can have issues. My dog was notorious for diarrhea when a young pup. You have to transition food very slowly. Also, vaccines can make them ill. Or there is the chance that pup is sick. Drinking is MUCH more important than eating. Is your pup taking water? Small amounts if their tummy is upset but frequently. And I would absolutely check in with your vet for guidance. You will want pup seen immediately if not drinking and inquire how long until they want to see pup if they are eating/vomiting. good luck and please let us know how your pup is doing!