Since a monthly withdrawal bleeding isn't a "real period", does it happen when you're pregnant? (heavy flow)

Are you withdrawing : ...From Progesterone pills or birth control pills? In either case heavy abnormal flow should be evaluated by your doctor.. Starting with a pregnancy test if indicated.

Usually not: Usually getting the withdrawal bleeding after stopping the active pills is good evidence that you're not pregnant. If you get heavier bleeding at the time you're expecting your period, it's hard to know the reason (fibroids, std, etc), but it's probably not from pregnancy.