Re: men and women
If a woman suspects she may be pregnant and has pain, it's important to check a pregnancy test: it could be an ectopic (tubal) pregnancy. These can rupture and lead to very dangerous internal bleeding.
On the other hand, cramps and low back pain can be caused by ovulation- the release of an egg by the ovary. In this case, of course, the pregnancy test would be negative, and the pains would resolve in a few days.
See your doctor if you're not sure.