Birth control

Okay so I had sex for the first time in a while again, and I had to just started taking my birth control again but I took a plan B just to be sure & then a couple days later I had sex again but I’m on the pill this time and I was supposed to get my period last Monday and I still haven’t got it? Could this be due to me starting on my pills again? Or could I actually be pregnant? I don’t know what to do