Ay, hi! So kung 1st day mo talaga ng pills on day 3 ng period mo, you're actually in the safe window, most doctors say taking it on day 1-5 ng period is okay and you're protected right away, so very unlikely na mabuntis ka. But since you're worried, best pag-usapan with your OB para sigurado, especially kung may specific concerns ka with your cycle o kung nag-miss ka ng doses before, mas mapapahusay niya kayo personally!