Could you give us a bit more background such as how old is the pup, is it drinking normally, is acting normal other than not eating, have there been in major changes in its environment or food, is the pup trying to eat but throwing the food up, is the pup current on its vaccinations, etc.

It is drinking normally he is 3 month

Is he trying to eat?

If he still has not eaten, you should consult your vet. Has anything else in his diet changed?