About a year ago I had problems with lower back pain which affected my legs. There was no diagnosis made after a scan, and as time passed the pain went. But since then whenever I bang my coccyx a painful lump comes up and swells considerably. After a few days I notice that a pussy liquid comes from it which produces an unpleasant odour, and the lump goes within a day or two. But then when I knock it again, it comes back.