I'm Taking Birth Control Pill (combination Pill) For Almost A

I'm taking birth control pill (combination pill) for almost a year and a half. Currently, I'm on my second week of taking it. However, today I don't know if I swallowed the pill since it is so small. I just had unprotected sex with my partner. I don't know if I should just take plan b. Am I going to get pregnant immediately? I'm really worried