Yesterday, about 1/2 way through the day, in gym, I noticed that there was a pale red bump on my lower shoulder . It felt like a bruise, so I just left it alone. The next day, It was no longer swollen, and the skin on my shoulder returned to normal color. But, there were little white bumps. One of the bumps had ripped open, and some puss was coming out, andnow my soulder hurts. What is on my shoulder? And what can I do to make the pain go away?