My first was posterior- and no one thought enough of it to tell me.
: My son was born "sunny side up" with his eyes open. I had persistent back labor for the entire thing ( roughly 20 hours total ). Most doctors apparently do not think having a posterior baby is a serious problem, I.E. they would rather you suffer and end up with a c/s so they make more $$$. Thankfully you have good practitioners who realize this is a problem. I wound up having a separated pubic bone and was unable to walk for about a week after delivery, and now suffer through my second pregnancy with pubis symphasis disorder. I do see a chiropractor regularly, and that helps to take the edge off of any pain I might be having in my back. I was beginning to have some sciatic nerve problems, but I started doing some exercises- mainly pelvic tilts, and the problem is resolved. The baby is also in the correct position, and I am soooo much more comfortable now.
If despite all your best efforts, seeing a chiro, doing exercises, talking to the baby, etc...lol the baby could still stay posterior. All I can really tell you is be prepared for some serious pain. The best position during labor for a posterior baby is on all fours, as this relieves pressure on the spine. Do NOT let anyone tell you that you can't be in this position. You will feel a tremendous need to "run away" from the pain, so you need to move around as much as your body tells you to. I highly suggest that you do not agree to constant EFM or being hooked up to an IV, as these things will not allow you to have free movement- once again, something that is NECESSARY when you're going to have a posterior baby.
Also, posterior babies can take a long time to push out. I pushed for 2.5 hours with my son, and thankfully DS's heartbeat was steady and strong through the entire ordeal, otherwise they probably would have sliced me open. So be ready for a potentially lonnnnng pushing phase. Being on all fours and squatting will diminish this and move the baby down faster.
HTH, and I'll be praying that your baby is in the right position!!!