DS 3.5 high temp and sore back

[topsi]

My DS has had a very high temp all night like about 40. He has a cough but is also complaining of a sore back on one side.
Obviously I am getting him to a Dr ASAP this morning but what could it be?
Chest infection?
Any ideas?

If its over the kidney area, could be a urine infection. Depends a lot on what other symptoms he has, cough etc. High temps make the joints/back ache anyway. Good luck at GPs

Thanks, he has a chest infection and has anti-biotics to take.