Suggest Treatment For Bruise On The Inside Of Thigh

I have a bruise on the inside of my left thigh. Though I do not remember injuring myself, it's very possible. The bruise was tender to the touch and red, but now it's purple and has turned into a ring, with a clear center. I'm 18, pretty active, no previous medical problems, and I've had one reconstructive surgery on my right knee, ACL and lateral miniscus.