I have experienced moderate pain in my left shoulder joint, expecially if I put pressure upon it, such as when sleeping on my left side, however, I noticed a swelling under my left arm and slight discoloration. I've examined the site and find no lumps, just soft tissue. I'm told that a swollen lymph node would form a lump or knot under the arm. I have had, during the last few days, occasional sharp pains in my rib cage area just below my armpit. I fear that I may have injured my shoulder and it's become inflamed or infected.

Any ideas of other possible causes ?

I intend to see my physician next week and seek their opinion.

Thank you,