I often get severe stomach cramp and back pain during intercourse. Ultrasound clear apart from a retro erred uterus. Is this the cause? What causes it?

The retroverted uter. I am not a Gynecologist, but I think the most likely cause is the retroverted uterus. Your uterus is facing "backwards." There's nothing wrong with it - you are just "made" that way (you were born with it, or it developed naturally as you did). The uterus usually points anteriorly (forward) and causes no discomfort as it presses on the abdominal wall. When facing backwards, it presses on the spine.