If you are young, it is possible to get a few irregular periods
. It takes time for periods to become regular. If you are facing some sort of stress
at home, this can also cause you to get late periods. Thus, what you can do is wait and see if the pills are causing problems. Also, some females have mid cycle bleeding. this is known as mittlschmerz reaction. This happens during ovulation. The ovulation then causes you to bleed every 16 days.
thus you will have 24 "periods" per year instead of 12. I hope this helps you. If bleeding is getting severe, then do consult a gynecologist.