What Causes Multiple Period In A Month After Taking I-pill?

Sir..I'm 20 years old girl. i had sex with my boy friend on 16th september,my period date was 3 on same month after sex i had i pill within 1\2 an hour after 1 week i had a vaginal bleeding the same month.how come twise in a month? today is oct.10th my period not yet come.am i pregnent am too worry pls give a advice