What causes recurrent chest pain while exercise or deep breathing?

Hello doctor,

For over a month now I have been having recurring upper chest pain. It is a quick sharp pain that lasts for a few seconds at a time. I mostly feel it in my sternum and sometimes on either the left or right side of my chest. I also get pains in either my left arm or right arm at times. Sometimes exercise or deep breathing makes the pain happen. I have noticed I have been burping more than usual lately but I have no sore throat or bad taste in my mouth. I have never smoked and I do not drink alcohol: no sickness, night sweats, or unintentional weight loss. I can eat, speak, and swallow fine, with no cough whatsoever. Last year I underwent an upper GI endoscopy for an unrelated reason and that was clear then I had a neck ultrasound for another unrelated reason and that too was clear. I suffer from health anxiety and I'm currently having therapy for it. My known conditions are irritable bowel syndrome and suspected B12 deficiency. I take 20 mg of Fluoxetine daily. I am really stressed. This is something like lung cancer or a heart attack and it is really stressing me out. Any advice is greatly appreciated.