Has your pup had his shots ??? also if he is really off colour you must take him to the Vet.You cannot take the risk,.with this tiny soul.He trusts you to look after him.
It could be something as serious (deadly) as Parvo Virus or it could be something relatively simple like a bacterial infection in his bowels. Whatever it is he will not last long if you don't get him to the vet immediately!! It's very bad when they won't eat or drink. Please get your puppy to the doctor now! Good Luck He may be saved!