Check out McGill's "Big 3" on core stability (
https://squatuniversity.com/2018/06/21/the-mcgill-big-3-for-...). He wrote the bible on lower back pain and strengthening, changed my life dramatically after having chronic sciatica for 5+ years.
McGill's program follows on from McKenzies older stretching program (which is fantastic in addition to McGill exercises).
https://www.spine-health.com/wellness/exercise/what-mckenzie...Research McGill and McKenzie and you'll almost certainly be able to fix your lower back pain.