Suggest Remedy For Swelling In Buttocks

A week ago, while cycling, I crashed, and the saddle hit me in the small of the back above the buttocks. Painful at the time, but fine by the evening. Since then there has been a big (bigger than fist sized) swelling at the impact spot. No visible bruising at first, but for the last day or two it has started showing purple. It is not painful at all unless I lie on it or press hard. No blood in the urine or any shooting pains. Normal movement, I have been out on the bike, and no problems at all. Should I be concerned that the swelling is not going down?