Fell Backwards On My Left Buttocks. Developed A Hard Knot

Fell backwards on my left buttocks. Developed a hard knot about the size of an egg, had to drive an hour to get back home and it kind of flattened out but still has some pain sitting on it - nothing visable as yet for bruising - am on Plavix so thinking it's a hematoma. Should I do ICE or heat or nothing.