"tsm" is so right about back problems and their variations. One cause of sciatica is Piriformis Syndrome which occurs when the piriformis muscle compresses the sciatic nerve as it leaves the buttock. It's very treatable and easily diagnosed by a competent PT or Orthopedic surgeon who specializes in low back pain.
One thing that most back pain does have in common is the cause of the pain and the implications of the seated position. The back muscles in there attempt to aid support to degenerative, ruptured and bulging discs, generate most of the non referred pain down the leg. Seating w/o motion exaserbates the problem.
That's where the "active motion" while seated comes in. Work by Mckenzie and his static exercise program has gone a long way helping back pain sufferers as well.
One thing you can take away from his work and "active motion" is, to continually adjust, every 10 minutes or so, a power/manual lumbar support and seat position while driving, a poor man's active motion if you will. The so called ideal seating position for you becomes less so w/o motion. This works even w/o chronic back problems if you a have a particular reason not to make stops and walk while driving distances.
Hopefully, move research like this finds it's way to the automobile seat so most of our back problems will be "behind us".