when i was a teen, my girlfriend had the same doubts. she called the hospital hotline for sexual related questions and they told her that if you took the pill correctly at the correct moment, meaning after the last day of your period, the protection begins right away with the first dose. this is because your ovulation cycle is over and the pill prevents further ovulations = prevents an egg being released from your ovaries which the next time would happen 21 days after your last day of your previous period. hope this helps