i woke up with a bright blue bruise on the inside of my arm below the elbow. it didn't hurt. then it looked like it was starting to fade but now it is a round grayish bruise that is sore and looks a bit red and a little hard in the center. if I rub it it becomes extremely dark then fades again. I get bruises all the time and don't know where they come from but this one is odd and in an odd place. anything to worry about?