My Seventeen Year Old Son Has Had Mono Three Times

My seventeen year old son has had mono three times and a sore throat several times. I have noticed he has no energy and usually when his throat gets sore his shoulders and chest break out with little red bumps really bad along with a short cough and very bad breath. The doctors keep saying the same thing. I've tried asking them is it possible for him to have an infection inside of his body because when he takes penicillin or gets a shot his back and chest always clears up until it's out of his system then he breaks back out. And he has no energy