My 8 year old son collided with another boy at football practice last evening. The other boy's forehead made impact with the left side of my boy's head, above his ear. My son did not lose consciousness, but fell down from the hit. He had a mouthguard in, but no helmet because it is flag football. He said he had ringing in his ears for about 3 sec.

He had a headache last night, but felt better after giving him one dose of Motrin (which I know now was a mistake to give as it has asa in it). He felt good this am so he ended up playing his football game today (on hindsight we realize that it was stupid of us to let him play football the day after a concussion). After his game he had a headache so we gave him Tylenol after I contacted the on call Dr. Since then he has had a tympanic temp. of 38.2-39 ℃ and a mild headache when Tylenol wears off. He has no other symptoms. I am concerned why he has a fever and if it is related to a concussion?