You could see an neuro, but your pain is consistant with SI joint
problems. As this has been going on for a while, you may have some arthritis
in the joint as well as inflammation. Ask your doc for some anti-inflammatories or arthritis medicines and see if those help with the pain. When sitting you could try a pillow or sitting on something very soft, like latex (sold in mattress stores), which will cushion your bottom and not press the bones together. Try not sitting for too long before getting up and stretching. Continue with the program the therapist gave you to maintain range of motion at the joint.