My Son Is 8 Years Old. He Is Up To

My son is 8 years old. He is up to date on all his vaccinations. As an infant he was diagnosed with reactive airway disease. The doctor said it may develop into either asthma or allergies. He never had any complications surrounding the RAD. He went to his well check ups but never had any reasons to see a doctor otherwise until about 6 months ago(around the time I placed him in public school instead of homeschooling). He has been to his pediatrician and urgent care numerous times with high fever, cough and runny nose. They always diagnose him with bronchitis and give him antibiotics. He completes the medicine and within a week he breaks out in a rash all over his body. The cough and runny nose come back along with body aches but no fever. His pediatrician says it may be a reaction to the antibiotics that causes the rash and will no longer prescribe the amoxicillin. Could it be something more serious? If it was just the rash I could accept it's a reaction to the medication but the cough, runny nose and body aches concern me.