Viral mostly .. or of mother are father any one at home are have similar complaints then it will effect kid regularly

Fever is a symptom of a problem like an infection in the body . So whenever there is fever we need to ascertain the cause of fever . Since you have not mentioned any other symptom i am assuming your son has only fever . Mostly fevers are due to viral infections . This is the usual manner in which fever behaves . It comes down when you give Crocin and then recurs once its effect wears off . In between the episodes baby remains active and becomes a bit down when fever is present .  These fevers subside in about 3 to 5 days . However as your baby is small and fever has already been going on for 3 days , I would suggest you take the baby for a review by the Pediatrician as many a times there may be subtle signs of an underlying serious infection which can be picked up by a professional eye