my baby has fever from 3 days .when he take medicine fever go for 5.6 hours.after that again he has fever why

A. because the duration of action of fever medicine is only for 6 to 7 hours your history tells us that the child is suffering from viral fever and in viral fever you have to give only symptomatic treatment that is for fever have to give paracetamol(max 4 times per day if needed) and plenty of water to drink and at least 60 to 70% of the regular diet and if the fever continues beyond 3 days then meet the doctor please do body sponge that is body wiping to decrease the body temperature with wet cotton cloth.