I can't relate, but i remember my mum telling me that her tailbone curled slightly at the end so when she was pregnant the baby put alot of pressure on it...the bad news is, on my way out I actually broke her tailbone and she couldn't sit properly for weeks after my birth. The good news is that I obviously moved it out of the way cos she didn't have any such problems with my younger siblings.
Anyway, hopefully that's not what's wring with you, but a possibility and at least it's not a threat to baby.