What Causes A Delayed Period After Taking Plan B?

Ok, so i've been taking birth control pills for about two years now. One day this month I thought I missed two pills, but i didn't and accidently took 3 pills in one day. Then my boyfriends condom broke after he pulled out. We used the plan B pill. Now i'm on my 3rd sugar pill, and haven't gotten my period yet. Am I pregnant?