ksdm, you've declined, so I'm not trying to convince you. X-ray doesn't reveal the entire picture as is clear in your situation. Even MRI which is more revealing, and I would request in your situation, doesn't tell you everything. Displacement of bone, ever so small, usually causes muscle spasm or muscle pain. SI joint dysfunction is rarely discovered on imaging because the movement of the joint is so small. Better than adjustments are the physical exam that chiropractor provide. Your pain sounds like SI joint to me. Your experience with PT and with imaging and pain are so like mine.
Accepting your thanks, and disinclination, I wish you the very best luck finding cause and remedy.