Whenever i cough or breathe hard, the left side of my ribs hurt. what could be wrong?

Musculoskeletal....: The discomfort you describe is likely musculoskeletal pain. The chest wall has bones, muscles, cartilage all of which is subject to muscle strain/sprain, cartilage inflammation and even rib bruise or fracture from excessive coughing. Once the cough is controlled, the musculoskeletal disorder(s) will also be controlled. So, see your doctor for diagnosis/treatment of the cough.