Thanks for asking at Healthcare Magic. I read your question and I understand your concern. Left side pain with hurting belly with persistent cough is due to excessive abdominal muscle contractions. In normal expiraion and inspiration only diaphragm and intercostal muscles are used while in cough and other strenuous situations abdominal muscles and other accessory muscles are also used. It looks like to be an allergic bronchitis. continue fluids, Mortin if febrile and also give him some safe cough remedy. If fever was spiking, cough was not subsiding for two weeks then consult your healthcare provider. Hope it helps best. Don t forget to rate this answer and close the discussion at Healthcare magic. Take your best care and of your son. Regards Dr Ejaz