What Could Cause Persistent Fever In A Child Despite Administering Calpol A Couple Of Times?

Hello my son is suffering from fever. I gave him calpol 7.5 ml as per his doctor suggested. After 2 dose at 4 hours. Fever is not reduce. So after 4 hours of second dose I gave him third dose. One hour passed after 3 dose still fever is same. Now I wish to give him mental p so can u suggest me how much mental p can b given and at what distance. His weight is 17 kgs