Could it be pregnancy

So i'm curious. I've been taking birth control pills for the last 3 months. Generally on the third day of the placebo pills, i start my period. I'm on the third day of the placebo pills on my third month, no period yet. I'm just curious though. If i don't get my period at all within these next 4 days, am I pregnant? I wasn't sure if pregnancy would prevent having a period even while taking placebo pills.