Hello.. My 9 Year Old Son Has Had A Mild

Hello.. My 9 year old son has had a mild fever for 4 days now.. Within this time frame he has had no cough, sore throat, vomit, etc.. He has only stated that his back hurts. He is acting normally. He just came into my room and said that his back pain is now in his rib cage (chest) and he cannot take a deep breath. Otherwise he seems completely normal.