Hi. I have an inflamed area on my tailbone that is spreading down slightly to the left side of my buttocks. I noticed it about a year ago at first, when it seemed like a small sack attached to the coccyx of my spine. Occasionally it has been inflamed and been painful for a few days, but usually went away after a week or so. This week, it has been worse than ever. It has spread, and now it is hard and inflamed and red, and visible. Is there some explanation as to what this could be? My only guess was some kind of a cyst. I was wondering if, since I am getting over mononucleosis, my body saw it as a foreign body and is attacking it as if it were an infection. It is extremely uncomfortable/painful to sit, drive, or use stairs.