I'm really worried about this chest pain I've been having around the middle part, along with some light back pain in the upper area. It's been going on for like 23 days. I don't have a cough, but I do get a lot of burping. A couple of months ago, I saw a pulmonologist because of some mild chest pain, and my x-ray came back normal. He said it was probably gas. The thing is, I used to smoke for about five years but quit two months ago. Could the smoking have something to do with it, or is it really just gas causing this pain? What should I do next?