Kate, I had an anterior placenta and posterior baby. I didn't actually know that Nicholas was posterior until he was almost out (which was probably a good thing)! It certainly explained the back pain I had, especially when pushing.

I really didn't find it to be that bad, my labour was 14 hours from when my waters broke, I had 13 hours of contractions. Yes, I had some back pain, but that was helped immensely by a number of things -

*the shower (there were two nozzles, one for my back and one for my tummy)
*the bath (this was the best! I saved it til last)
*heat packs applied to my lower back during contactions (DH's job)
*massage of my lower back during contactions (DH's job)
*walking around, and rocking my pelvis while leaning forward

Obviously I didn't do all of these at once, but I just went with what felt right at the time. Here is my birth story if you want all the details Nicholas John's birth story (very long!)

I really hope that your bub ends up being anterior, but if not I hope that info helps