I too have a bad back and neck from a car accident, and since the birth of my 2 girls 4 & 6 years ago my hips have never been the same.

I hugely recommend chiropractic with a GOOD chiropractor, and you need to go more than a few times. I've been going for 3 years now and the improvement is HUGE. I no longer drag my left leg, and I can actually look up and see the ceiling.

Something that may help you greatly is doing piriformis stretches:

http://www.halhigdon.com/15Ktraining/Stretch.htm

I've learned to always stretch before I ride (including trail riding), and it really helps. What also has helped is I purchased some very wide stirrups with these pad things in them for my western saddle; they take up the shock. But I'm still most comfortable in my Max Hofpner dressage saddle.

Good luck, back pain sucks.