(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.