What are the chances?

I started having sex with a guy last week, I’m on birth control and I take it at the same time every day.

My period is due today-ish (sometimes it start a day later cause of birth control) and it hasn’t shown yet, and I have a bad stomachache and feel quite nauseous and dizzy.

I know the chances of ending up pregnant are super low, and if my period doesn’t show up in a day or so I’ll take a test, but what are the odds I’m fine?