Welcome to HCM,
It seems that it is viral fever
Wait for 1-2 days more and he will be alright.
Give enough water and liquid so there is perspiration and will help temperature going down.
If you give Calpol
syrup but not enough water fever may not go down.
If there is no respond and after giving Calpol syrup, fever goes down for few hours and again temperature rises, then consult your doctor and go for investigations.
Ok and bye.