Had an abortion 3 weeks ago and started taking birth control the day after.. now i seem to have my period and having heavy bleeding. is this normal?

Probably: I would expect you to have a period 3 weeks or so after you started birth control. So the timing is normal. Heavier than usual bleeding with the period following either a miscarriage or abortion is common. Whether it's normal depends on how heavy the flow is, how long it lasts & whether you have other symptoms, like light-headedness, with it. Please contact your your provider.

Period: Yes it is time for your withdrawal bleed on the birth control pill. You take 21 days or 3 weeks of active pills then placebo pills in which you have your period.