When the river runs red
There actually is a Goddess of Menstruation in Egypt.
Sekhmet was created by Ra to kill off the humans who were conspiring against him. After almost wiping out mankind, Ra bade her to stop but she could not as her bloodlust was unquenchable. Ra then tricked her into drinking from the Nile by turning in Red. As she gulped down water from the Blood red river, he turned it into beer which intoxicated her and sent her into a deep sleep. When she woke up, she had no recollection of what had happen. She became a benevolent goddess then.
I still cant get over the fact that she is a goddess of periods. I wonder if pms counts. Hahaha..