Where is this severe lower back pain coming from?

Let's count the ways: Referred pain from hip or si joint, vascular, genitourinary, gi, tumor, infection , gynecological issues and then back issues: tumor, infection, rheumatologic, disc, facet joint, fracture, deformity, muscular, deconditioning, degenerative, spinal stenosis, epidural hematoma, instability to name the majority.Of causes.

I agree with : Dr. Dowlings answer he provided. I would add from a podiatric perspective flatfeet or "hyperpronated" feet can be a definitive cause as well, as the foundation of the skeletal structure becomes misaligned causing increased lower back strain.