How To Cure A Pea Sized Knot At The Back Middle Portion Of Leg?

I have a pea sized knot on the back middle portion of my leg. There is no pain, just a knot. I had bruising there that I am not sure how I got unless it was from prolonged sitteng for 15 hours. Could this be the result of sitting for thtat long? Should I see a dr? Could it be anything to worry about? I am 42, 5 8 and 109 pounds if that matters and in very good health and pysical shape.