What is the physiology and the cause of the pain in the lower back in women? Is it related to uterus and gynaecological issues? If so, my doubt is, why there should be a pain the back while the uterus is located more ventrally? How the pain is related to the menstruation and periods in between?

My understanding is that it is just a result of uterine contractions, which radiate pain throughout the nerves in the pelvic region, which includes lower abdominal as well as lower back pain.

Referred pain? Like when people feel pain in their left shoulder and/or jaw when having a heart attack.