Suggest Treatment For Fever And Low BP

My son is 15 years old, he had a fever starting Friday night until yesterday this morning. He has always had large tonsils which seem to get irritated every time he gets sick. This afternoon his fever disappeared and now it seems like it's below normal, it's been running between 96-97.5. I took his blood pressure (digital) and it read 89/51, which seemed a little low to me. He feels fine with the exception of his throat feeling irritated.