Both of my younger 2 were posterior. Both labours were extremely painful in my back. With DS I was put over a bean bag & that relieved the pain instantly.
Unfortunately he was distressed to, so I had to turn over to be monitored. But it helped. Both labours were drug free! Well I demanded pethidine with DS, but it didn't kick in til after he was born.
I rocked on an exercise ball for 2 - 3 hours to turn DD2 around!