Concerning your chest pain – it is concerning that it is persistent. Given your young age, the most common cause might be the muscles in your chest wall. Heart problems can give rise to chest pain, but not persistently. The thin membrane that covers the lung, called the pleura, can give rise to pain, but usually not persistent. You should see your doctor who might decide to order a chest x-ray and other tests. You should be prepared to answer questions like these: what makes the pain worse, what makes it better, is there a position which alters the pain or a movement of your chest or arm, describe the nature of the pain – pressing, dull, burning, sharp, etc, does it awaken you, is it associated with sweating, nausea or skipped or irregular heart beats, does the pain go anywhere else, point to the area where you feel the pain – is it a large or small area, does it get worse when you cough, how long does the pain last, does the pain get better or worse with eating?
Concerning your cough – if the cough is productive of phlegm from your chest – does your doctor think that it is from your reflux? Usually a chest-x-ray and a simple breathing test called spirometry would be performed. Examination of your sputum might be helpful as well. It sounds like your doctor has evaluated this thoroughly with the chest x-ray and CT scan, which along with exam of the sputum would be the best way we have to exclude lung cancer. However, if your symptoms persist, your doctor might want to repeat those tests now.