What Causes Bleeding After Taking I Pill A Week Of Menstruation?

i had sex just after 1 day when i had finished with my periods then i took i pill within 6 hrs and after 3 days i had my periods again and that period was of only three day. i want to know that is it fine or i will get pregnent or not? i use to get my periods around 24th of every month so i will period on the same date or not?