How To Treat Nausea,fatigue And Vomiting After Being On Antibiotics For Strep Throat?

My 14 year old son just finished a 7-day cycle of antibiotics to treat strep throat. His throat is no longer bothering him, but he is still not right. He is fatigued all the time, but cant seem to get a good night's sleep. He is nauseated, can eat, but if he doesn't lay back and relax after eating, he vomits. Any suggestions on what could be the problem?I am taking him to his doctor today.