I have a daughter who experienced the same things when she was around your son's age. The doctor kept giving her antibiotics and saying that she would grow out of it. She never did. So, at 21 she had her tonsils removed. End of infections. It turns out that because she had large, pock-like tonsils, the infection never really went away - it hid. I'd say see an ENT doctor (ear, nose, and throat) for a second opinion. By taking all those antibiotics, he is building up resistance to that family of meds. Hope this helps.