The cause of the ear pain needs to be evaluated by a doctor. Kindly take your child to see an ENT doctor for management.

How did you confirm the high temperature?
If you used a thermometer and not hand feeling and the temperature is above 37.5 degrees, give paracetamol and head out to the hospital

It is not normal to sleep with the mouth opened. He seems to be experiencing enlarged adenoids. Kindly see a Paediatrician or ENT surgeon for further evaluation and management.