I'm afraid all we can offer is the usual advice of some Atrosan® Devils Claw taken internally, some Atrogel® Arnica applied externally and some supplemental magnesium. In combination, these might well help control the pain and tension in the muscles.
As you've already seen a physical practitioner and had little relief, would you consider asking your doctor for a scan, as your problems might have their origins in the joints, perhaps in the pelvis or spine, for example.
Do you have an occupation where the back is overworked due to lifting or perhaps you're sat in a poor position at a desk? Ask your employer to arrange for an occupational therapist to visit.