SIJ dysfunction can cause pain upon lying down (rolling around in bed), sitting to standing, sitting for prolonged periods, or standing for prolonged peroids. If the SIJ is not functioning properly, the altered biomechanics can cause compensatory patterns above and below the lesion? (muscle tightness being one of them). Why was an X ray not taken? If anything sinister were underlying would it not be wise take one?
SIJ pain can be ruled out through the following; motion palpation, static palpation, (difference in movement, oedema findings) history findings with the above clues.
Also does the patient have a short leg? Anatomical or Functional. Flat feet? Also check the functionn of the rest of joints in the spine.
Neurological testing can produce no postive signs even when a disc lesion is present.