How Can A Large Thigh Bruise With Soreness Be Treated?

I am 32 years old, 5'7" and 137 lbs. After my second child was born I noticed what I thought was a large bruise on the back of my thigh. It is a rather large, raised, welt, about the size of a large handprint. One and a half years later, it is still there. It does not itch, but feels a little tight and sore.