hi, i just recently quit smoking, like 2 months ago, and i smoked for about 2 yrs., i am still coughing, so i went to the doctor and i got a chest xray, it came out clean, what concerns me is when i cough, i feel like pain in the middle of my back, i dont have problems breathing, nor does it hurt to breathe, could this be the muscles on my back? should i be worried?