Thanks for writing your query.Back pain
can be due to myalgia
as an effect of fever, mainly viral.
It is advisable that you get the following investigations done :-
1. Complete Blood Count
3. Test for malaria
4. Urine examination (Routine/Microscopic)
You can continue giving Paracetamol
500 mg three to four times a day. Sponging with water will reduce the fever.
Ask him to take proper rest and to drink plenty of pure filtered water.
Treatment can be reviewed after the investigation reports.
I hope this is helpful to you.