Sever Back Pain During Mensuration, Bowel Movement. Relief With Heating Pad, Painkillers. Reason?

Since i was very young i have had sever pains during menstaration, while having a bowel movement . Now for the past year i have had sever lower back pain on the right side during menstaration. That gets worse during a bowel movement to the point that im doubled over in pain and crying. The pain is a dull, gnawing, aching that radiates down the back of my leg. Its is only reduced by a heating pad or a lot of pain relievers. It even wakes me up in the middle of the night, every night and prevents me from sleeping. I dont not have heavy periods, in fact they have always been light without to much discomfort. Recently i have been off of birth control and the symptoms have escalated. I do not have a regular physician that i see, and the emergency room wont help me get to the bottom of this. I cant live with this pain anymore. What Could this pain be? Please help.