What Causes Burning Sensation Below The Armpit?

Chest aches.
Hello, I am a 33 yr old female. I do smoke, in the process of quitting. Down to 3-6 a day. I also have bad anxiety/panic attacks, for 5yrs now. About 2 wks ago I started experiencing chest aches on my left side just below my breast. This was on an off through out the day everyday. Sometimes I felt it above my breast, on my right side and in the back area. I went to see a doc about a wk ago. Said my lungs n heart sound good did a small EKG and said it was normal. I was put on Famotidine 20 mg 2x a day, for acid reflux, Xananx 0.25mg for my anxiety(I only take it as needed). The aches seem to have lesson somewhat but I awoke yesterday morning with this burning feeling when I touch my skin on my left side just below my armpit right across from my breast. I can't quite make out if there is possibly some swelling in the area, if there is its very small. When I went to the doc I did not get a definite reason for this infrequent ache. With my anxiety this issue has caused my anxiety to become worse. Im constantly thinking about what can be wrong, and most times thinking the most awful things. Every little ache on that side around that area including my face makes me want to panic. Constantly thinking it being my heart or lung cancer. Because of this im finding it even harder to relax and ease my wondering mind. I really hope you can address my symptoms properly and tell me what is going on. Look forward to hearing from you. Dawn