Warning: Dumb question

Y’all I’m about to sound illiterate asf but I have this question and I’ve been wondering be it has me like

When you take birth control, you don’t ovulate, so you can’t get pregnant. So why do some people get pregnant while on the pill?

Anyways, so when we get our periods, where does the blood and blood clots come from if we don’t release an egg? Mhm??

Dumb i know but I’ve been wondering lmao