If you are having any other gynecological problem like fibroids, then that could be the cause. Have you got checked for it. My friend always used to have such terrible pains and when she consulted the gynec, she was told about this fibroid in her.
I would have to agree with that because i have the same symptoms and i have fibroids. I t can cause pain in your back, neck, stomach, breast and thighs. It would give you symptoms as if you were pregnant.