Hi Belle,

I know what you're going through only too well hun!! My bub is 2 wks old and he was posterior as well. The back pain is labour was in a league of its own, he didn't actually spin until his head was out. But, the good news is that he was born vag (no c-section) and no tears. If your bubs doesn't spin, what worked for me in labour was put the fitball in the shower with a towel on top of it (so you don't slip off!) and lean forward and roll your hips from side to side. This with hot water running down your back is heaven!!
Good luck babe!