Suggest Remedy For Purple Bruise On Buttock After Injury

I fell down some stairs and landed hard on my right butt cheek. This was three days ago and the bruising has gotten bigger and more purple each day. Right now it is about 6 inches wide and 3 inches high. Is that normal or shouls I go have it checked out? My back and shoulder were a little achy, but seem to be getting better. Besides the normal pain of a bruise, nothing else is bothering me. I am female, 43 and 140 lbs.