I had a lot of lower back pain after I injured my knee many years ago, mostly just a painful stiffness. I found a combination of stretching and heavy SLDL's helped me a lot. Stretching exercises I would recommend: toe touches, ballet dancer stretches, stretch kicks, splits, tai chi swinging arms. A lot of the stretching I learned studying Karate and Tai Chi. You might want to try out some martial art schools if you have time for it.