Hi, I Have An Open Sore, Near The Crease Of

Hi, I have an open sore, near the crease of my leg and my groind. Its a red open sore with a flesh colored raised bump at the top. It was very painful for a few days, then the pain completely went away about a week or two ago, now im just left with an open sore, with a few red patches around it, just red spots, not bumps. There is also a brownish, blackish patch under the sore. What could this be?