@araney... Postural drainage can best be explained on you tube, but I'll give a short explanation. My mucous is produced in my left lobes, so I lie down on my right side to help it drain out. This makes coughing much more comfortable and I listen to books on tape.
If you try both sides you can find out where mucous comes out most easily. Give it 20 minutes or so. When I had frequent CT scans and bronchoscopies, my doctor told me which lobes were active or infected. I was able to clear out my MAC infection , then a candida infection. Right now it is every day maintenance to prevent infection and works very well. I've never had to use any of the contortion type postures. Plain old lying down works fine. Best of luck with it and your back pain should improve.