What Causes A Bump In The Tailbone?

hi I have had a bump about the size of a quarter on my tailbone. It has been there for about 9 months. When I touch it, it does not hurt but just feels weird, I can move it around a little bit, and when I press it I get a faint burning sensation on the tailbone. I broke my tail bone about a year ago, not too painful, just uncomfortable, I dont know if that this the cause but does anyone one have an idea?