Thank You. I Have Had Two Episodes Of A Large

Thank you. I have had two episodes of a large lump (the size of a of a small apple cut in halves) arising in the space between my right pectoralis and deltoid. In the first episode about six weeks ago, I had a CT scan of the lump which had reduced by 80% on it's own prior to the scan. No conclusions. It finally disappeared. I'm four days into the second growing lump and it is not debilitating but uncomfortable. I've had two rotator cuff repairs and a reverse shoulder replacement on the same side but this is lower and more into the upper pec just below the collar bone. One common denominator is that these lumps seemed to start a few days after using a pec/fly machine while exercising. What is it?!! Thank you. Larry