What Causes Swollen Rash On Inner Thigh?

i have a rash that developed on my left inner thigh. High up on leg. Not in crease but close. Just below where leg meets groin area. I run and one day I did squats, so legs were tight...i.e I walked a little funny cause legs burnt from squats. a few day later when muscles seemed to be better, I was still walking funny and noticed a rash. I treated with lotion and then some powder. The next day I notice that the rash is swollen. It had a small head form, but when I cleaned, I removed some yellow pus and then some bloody liquid. Keep cleaning it and have even put some cream on it. It obviously hurts when it rubs as in walking, but also when I initially sit on that side. Any thoughts as to what it is, what caused it and how to treat it? Thanks