Any idea why my tailbone hurts

I did not hurt it. I have not fallen, been hit, anything like that. I do not understand how my tail bone would inexplicably hurt very badly. Also it hurts even more when I climb stairs or a ladder. This is driving me nuts! I can't even bend over to puck up my 1 year old because it hurts so much. Does anyone have any suggestions as to what may have caused this???