I suffered with lower back and hip problem for a few years. I thought it was sciatica. It turned out that my hip kept slightly dislocating, which then caused lower back problem. In hindsight, it might have been caused by IBS syndrome which kept pulling down the hip joint.
For me, core and hip exercises were the most beneficial. And, stretching as well. I think core and hip strengthening exercises are often overlooked, but this is very beneficial for your movement and ground strokes.