What Causes A Lump Under The Skin With Sore And Bruised Leg?

i fell off my steps a week ago tuesday, and my leg is still sore and bruised (blue). It still hurts to put too much pressure on it, but what worries me is there is a knot like bump under the skin that I can feel with my hand and when I sit on it. I still have to lean on to the right side so as not to put pressure on that spot as it burns if I do lean on it too long (minute). What is the bump under my skin which hurts?