The cause of lower back pain can be difficult to pinpoint,
I have seen a number of physio's, chiro's, and osteo's regarding my lower back pain and they all can't give me a straight answer. I have had an X-ray, but have not been sent for an MRI.
At the end of the day I think lower back is ambiguous. One must just do what they can do to avoid things that make it worse and do those things that can make it better, and this can take a lot of experimenting which is probably the most frustrating part of it.