Yes, day after pills are also hormones. There are high chances it's the reason your periods are postponed.
The entire process of menstruation occurs, due to hormones, mainly estrogen and progesterone. They act on your endometrial, ovaries and breast to bring in the entire process of menstruation. When you have the birth control pills, these are hormones which will alter the process of menstruation leading to irregular periods.
You can wait for a week or two; your period's pattern will set in after a month’s time. You don't have to be anxious about it. Meanwhile, I would like to advise you to go for protection like condoms rather than birth control pills. You are only 16 and these pills do have their baggage of side effects. Always use condom when having sex.