Firstly, check out www.spinningbabies.com for some great tips on how to get baby to turn. You really have to persevere with it if you want to be successful. I also had the same problem as you with my last pg and had weeks of prelabour in the lead up to his birth. I went and had some bowen therapy too, which I had some moderate success with, but he turned back to an OP position. If all of that fails, it is possible to birth a baby in the OP position, and some of the techiniques on spinning babies are for use in labour, but you will have to work hard to get them to turn. Some babies will turn during labour and some wont, and shoulder dystocia can then be a problem (as it is a positional issue, not a size one). Lots of lunges, squats and all-4's positons can help during labour - I even found sitting on the loo to be helpful as it opens up the front of the pelvis.