I have what looks like a small bruise on the front of my shoulder. It is no bigger than 2cm and is slightly indented. I first noticed it over 5 years ago and thought it was a stretch mark. It typically gives me no pain. Last night is was bothering me when I laid down for bed. I pinched the tissue and a bulge formed in the area and it became painful. Using moderate pressure I pushed on the bulge which cause a sharp pain but the resulting bulge went away. Do you have any ideas of what this could be?