(adjective) When a woman is "on the rag", that means she has her period. She's also likely in a bad mood because of the various discomforts associated with pads, leaks, tampons, washing out
underwear, not being able to wear
light-coloured skirts or
pants, etc.
She's really in a mood, she's on the rag and complaining about everything. Last
night she
slept so soundly that she woke up in a
pool of blood.