What Could Cause A Recurring Bruised, Painful Sensation With Discoloration At My Coccyx That Makes Sitting Difficult?

I have an odd bruised feeling on the upper part of my butt crack. I have had this a couple of times too. It just comes and goes. It also has a slight bruised color line down it. But I could never figure out what it could be and how to avoid it. When pressed on it is extremely painful and disables me from sitting certain ways. I ve also tried to massage it but putting pressure hurts to much.