Back in October, my back went to hell in a rowboat. In one fell swoop, I went from riding centuries to riding in the electric cart at the grocery store. I was on crutches for a month. Maybe more.
I'll spare you the boring details, but if you've got back problems, you may want to consider two things that really helped me a lot.
1) Yoga. Ya gotta be careful to stretch without overdoing it. A good instructor or video will show you how.
2) Pilates. It's pretty subtle, but I find it really helpful. You learn to build core and back strength. And a good teacher will show you how you ought to be positioned on the bike.
I'm still taking baby steps, but I did a 12-mile pain-free ride today, and that really bolsters my spirits.
By the way, I realize these suggestions are not a substitute for a physician's care. But I just thought I'd put it out there for your thoughts and discussion.