Can someone explain this to me?

So i am religious about taking my birth control for the past couple of years i take it the same time on the dot, i think the latest i’ve taken it has been 3 minutes. However, the one thing i’m confused about is how during my placebo week how am i still protected. My boyfriend and i usually use condoms but we’ve been dating for a year so we sometimes don’t considering i’m really good with my birth control and he pulls out well every time. But recently we had sex on my last placebo pill and i just need someone to explain to me how i’m still protected...does anyone know?