I'll second the deadlifts suggestion. Seems kind of contrary to what you would think to address back pain, but it worked for me. I've been struggling with major back issues for 25 years. I've had injections, ablations, all kinds of therapy, decompression, chiropractic, and acupuncture. The thing that seemed to work the best was simply lifting weights...particularly deadlifts. Doctors will tell you it's a bad idea, but if done properly they really help to strengthen the entire posterior chain. There really isn't another exercise that does it better. But be careful, it's very easy to get carried away and end up pushing yourself too much and injuring something.