Irregular period and unprotected sex

hey about 3 weeks ago i had unprotected sex my bf did not pull out so about an hour later i took Postinor .now 3 weeks later im getting what seems like an early period. However it is very irregular. It started on saturday night with cramps jus like my period would, very light in flow and color. I woke up sunday morning and it was gone it returned later sunday evening accompanied by regular cramps. for the past 5 days it has been off and on my breast are still very tender, usually once my period starts they would stop hurting me but now they still are, and ma actual period is due this saturday.
should i be worried or is it jus a side effect of the pills?
am i pregnant cuz i am very worried