I suffered from chronic, low level back pain for years. Due to poor posture and heavy lifting. Then I slipped a disc in my lower back. Lived with that for a year before seeing a doctor. Gained weight, problems got worse. Became less active. Eventually found a good sports medicine doctor but by that time I had even more pain and was hardly able to walk because of piriformes syndrome - locking up of the muscles around pelvis/hips to "protect" the back. Had series of steroid shots by a pain specialist which allowed me to walk again. Took lots of pain killers. Tried physical therapy. Quit riding pretty much. After two years, the bulging disc self-healed. Then I started waking up w/ tingling arms at night. Found out I had degenerative disc disease in my neck. Sort of a wake up call, no pun intended. I still needed to cut back on heavy work. (years ago I had driven horse carriages/worked farms, overdone it). Tried to avoid heavy lifting, no pulling by horses, eased back on training my horses and hired someone to help me part of the time.
As I was able to walk more, I lost weight, and some of the "stabbing" pains I'd been feeling in the middle of my back went away. They were due to being too "heavy" on top. Sports bras/better support was the answer as was weight loss and improving posture. I had some shots for the neck pain...
As for how I got riding again - I stayed away from sitting the trot - backed off from widing wide-backed horses which made my hips/back hurt - rode for shorter distances on "narrower" smooth horses - didn't ride anything that might throw me - stopped playing rodeo w/ horses (at one point I had stress fractures in my legs and one ankle and was wearing a "boot" but still was riding w/ one foot in the saddle and playing around and that jarred my back more).
Then last year I bought a Peruvian Paso and now I'm getting ready for 50 mile rides. I have gotten completely off any pain killers or shots - and take Advil routinely for any soreness. But mostly I can ride without pain, altho my neck still bothers me if I'm not careful. My doctor says it is going to get worse. I hope to avoid surgery.