Lower back pain can be generated by the disc, facet, bone and nerve but in your case, I believe the differential is disc and facet. Standing/walking can lean more to facet than disc. Hopefully, the pain is more facetogenic than discogenic due to the easier treatment of facet pain.
The first step is physical therapy. a good course of 2-3 months can be helpful, especially if it is pilates based and you do your homework. If ineffective, then a series of diagnostic facet injections can reveal if the facets are the true culprit. If these blocks are effective (please read all hyperlinks to understand this and have the injectionist also read these), then you are a candidate for radio-frequency ablations (RFAs).
https://neckandback.com/treatments/facet-blocks-and-rhizotomies/
https://neckandback.com/treatments/diagnostic-vs-therapeutic-injections/
https://neckandback.com/treatments/pain-diary-instructions-for-spinal-injections/
Dr. Corenman
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.