I had shoulder surgery Friday June 8, and I tried to shave my arm pit prior to post op visit 1 week later.  A day later I noticed a small knot under my arm, itching and painful.  Then two more lumps, red and swollen.  My arm was in a sling and the first week I wore sleeveless and shoulderless shirts to make dressing easier, but arm pit moister did seem to be a problem.  I tried very hard to keep the area clean.  I had used deoderant after shaving, but it was a natural crystal water based kind.  I have since stopped trying to use anything but just keeping it clean. Should I be concerned?  I just want them to go away because they are painful and uncomfortable.
They may be swollen lymph nodes which become painful when there is some local inflammation and in your case, it is surgery of the shoulder. You should take antibiotics and painkillers for the same. Also, it will be better to show it to the doctor who has performed surgery to rule out any infection in the surgery site as it may also cause this problem. For keeping your underarm Chat Doctor.