Lemme preface the injury a little bit. In 7th grade I went on a snowboarding trip and during the trip I feel flat on my ass on hard ice. Throughout the next year and a half~ I found that whenever I would sit a certain way (back straight, or leaned back, was fine when I crouch over and sit mainly on my thighs) for an extended period of time it would hurt quite a bit when I get up, some dull pain for about 10~15 seconds, I presumed I bruised my tailbone and got on with mah life. I'm now a freshman in college and throughout the past few years it would come back off and on for a few months at a time, and now it's happening again. I have to shift every 10 minutes or so because it gets uncomfortable and every time I shift the pain comes back, but goes away once pressure is put back on. So... any diagnoses/suggestions?