Hi my son has a fever and cough since monday he doesn't want to eat or drink anything he has fewer wet diapers than usual what can I do?

Talk with doctor. Infants who aren't eating and drinking may quickly become dehydrated. Your doctor will take into account the baby's age, how long he's been sick, when he last had wet diaper, if there are associated symptoms like vomiting/diarrhea. If dr. Agrees it's ok to treat at home, try giving an oral electrolyte solution like pedialyte, by a medicine syringe, about 2-5 ml every 5-10 minutes.
Rectal Tylenol (acetaminophen) Try tylenol (acetaminophen) suppository to control pain and fever and try pedialyte to encourage oral intake. The fewer diapers suggests dehydration.