Have you considered an intra-articular hip pathology or possible iliopsoas strain? Labral tears have been known to refer superiorly into the lumbar spine - or associated with maladaptive gait patterns with subsequent NSLBP. Beyond that from the MOI I would be thinking Lx first (more likely facet) andSIJ second. If its purely an acute muscular injury (i.e. strain) I would have expected considerable improvement in 1/12.