Thanks for query,
I think your Doctor had given you a right advice.
This flow of menstruation
happens as it is a withdrawal bleeding & your hormonal
level has disturbed by taking I pill.
as your pregnancy
test negative nothing to worry.
if you have heavy bleed & not stopped after 3-4 days of now then you need medicine to contract your uterus
with some vitamins to help clotting of blood.Thanks