I've dealt with back pain for 15 years or so. It got to be quite debilitating for a while, but I always pushed through it and tried a bunch of things without much improvement. At one point about 4-5 years ago, I went to a chiropractor who recommended that I do a series of stretching/strengthening exercises put together in a book called "Foundation".
I was skeptical at first, because I'd tried strengthening the core with ab workouts, back strengthening, etc, and nothing worked. However, after doing these particular exercises regularly for a week, my pain reduced, and flexibility increased significantly. I got to the point that I no longer needed to go get massages, take advil, go to the chiropractor, etc. Now, years later, anytime my back pain starts to come back, I do these exercises again for a few days and the pain and stiffness go away.
The exercises themselves are a little awkward and funny looking, but they really worked well for me. I know back pain can be caused by a lot of different things, and there's not one solution that fits everything, but IMO, it's definitely worth trying.
Here's the book that goes through the exercises in depth, along with explanation of why these particular exercises work. I bought it and enjoyed it.
Here's a video showing some of the exercises (I told you they look goofy).
Hope this helps, and feel free to reply back or DM me if you have any other questions.