My oldest son had it when he was in 8th grade. Same as you, he came home from camp, thinking it was allergies, asthma. . . until the day he was coughing so hard in the shower, he didn't mind me coming in and seeing him naked, at age 13. I really thought he was going to die. DH, myself, and DS #2 had to take the antibiotics and also inform his whole team at school and his grade at religious school to get tested.
It turned out he caught it from another kid at camp. DS had his first Dtap shot at 2 months old and actually had one of those "unusual high pitched crying" reactions, so the doctor did not give him the "p" part for the rest of the shots. They wouldn't give it to DS #2, either. This was around the time when a lot of information about reactions to this shot first came out; I am not anti-vaccine at all, but after I described the reaction to the pediatrician, he was freaked out as I guess this was connected to possible neurological side effects.
It took my son a full 4 months to recover. He was weak, pale, and generally unhappy for the entire fall.