I have very tight hamstrings (can only get to within about 10 inches of my toes trying to touch them) and have had lower back pain at various points in my life (such as after playing hooker at Rugby or cycling).
Stretching the gluts seems to sort it.
Stand up with your back straight and a good lordosis (the concave curve in your lower back), and then bend over to touch your toes, but keeping that straight lower back, rather than bending over from the middle of the back like a question mark, like most blokes.
You will feel tension in the back of your legs from the hamstrings at the knee right up into your gluts.
Hold the stretch and feel the gluts loosen up.
I have to do this sometimes when shopping with the wife, although she makes me go elsewhere in the store to do it. But it works.