Sciatica and pain Dam Back .. Help

like others in this thread, I've had a bad back for most of my life- I've never found anything that helped, so I've also learned to live with it (lots of hand-on-the-knee when trying to pick something up off the ground lol). The 'heavy duty' painkillers barely take the edge off.
When I was younger, I used to do 400-500 sit-ups a day, and during that period I never had back pain (as my abdominal muscles were doing most of the work holding me up). But as I got older (and lazier) I quit doing that, and now it's back to having back pain almost all the time.