I have also dealt/ dealing with lower back issues.First and for most pin point the issue first then give this some thought….
When you tweak your lower back (L1-L5) your bodies innate response is to protect the spinal cord and limit ROM. Your psoas(starts at L1) will tighten up right away to protect your spine from deviations. Once that happens your extension/ flexion will suffer. The psoas is also your biggest hip flexor. It being tight can in turn start to affect your other hip flexors, sartorius,from functioning properly like iron tiger explained. Getting that muscle to relax will do wonders for your low back and hips. Try some of the psoas smashing mwods.
Hope that helps