What Do Purple Colored Bruise On Buttocks And Knee Indicate?

About 1 week ago I noticed I had a very dark black/purple round in shape colored bruise on my right butt cheeck; however, it did not hurt at all, even if I pressed on it. I do not remember hitting myself. A bruise of thet nature you would think I would remember. Then today I noticed a bruise not as dark still black/purple on the left side of my right knee. It does not hurt at all, even when I press on it. Same thing, I do not remember hitting it and this one is fresh. I am 41 years old and I do take anti-blocking medicine for migrianes. It it topamax 100 mg 2 x a day and I take 20mg of dicyclomine 2 x a day for IBS and 10 mg or Lexapro. For the pain med. for migranes 40mg of Relpax as needed. I will take Ibuporen/tylenol as needed. In the past I was dig. with a 1cm cyst in my liver and every year I do get my blood work done and a MRI and my liver enzymes have never been high and the cyst has been the same size for 10 years. Can anyone help.