Help!!!

So this last month i've been not so perfect with my pills which is really not like me since im so sexually active, but it's been a busy few weeks. Anyways my boyfriend and i have sex VERY often and never use a condom because i'm on the pill, but last night he came in me by accident and i'm really worried. We immediately went to the store and got Plan B and i took it right after. I was supposed to get my period today and i didn't, is this because of the plan b? And what are the chances i could be pregnant? I'm really worried