What Causes Fever, Throat And Back Pain?

Hi Doctor, My son has had a fever of 100 - 102 off and on for about 3 days. Not much of an appetite, fighting allergies a little, active at times but extremely drained at times. Completely unlike him, he is normally very very active. At times just wants to lay on couch or bed. Went to Dr to day said ears and throat looks fine and at the time no fever. Since the visit he hasn't eaten much, played some but same as past few days. He just told me "don't touch my back that hurts". I was shocked. I finally narrowed it down that it hurts all the way down his spine. I asked if he hurt anywhere else he said no except my throat. Fever of 101.3....... Please help, don't want to sound like a crazy mom, but I am concerned because I have never seen him act like this.