Sultana - for future reference, the most physiologically dependable way is Abaya's way - orgasms cause contractions of the uterus, which cause it to eject material (if it's going to anyway, it's not like an orgasm will eject a baby or anything!).
The lack of prostaglandins is what causes the lining to shed and the uterus to contract. Ibuprofen (motrin, advil) block the prostaglandin pathway - great for cramps, not great for getting the bleeding over with. Also something to keep in mind.
Cheers!