Thanks for choosing HCM.
Your son may be having a viral infection, which generally is self-limiting.
Apply some calamine
lotion on his rashes & give him an anti histamine
Continue with paracetamol
that you are giving for fever
He may be encouraged to drink plenty of warm liquids & avoid oily , spicy foods.
If the rashes & fever do not subside in a week get him investigated after consulting a doctor.