Pregnancy Chance? Why is my period late?

Brooke
On April 1st, I had sex with my current boyfriend and it's the only time we have made love. He didn't use a condom but he did pull out and 2 days later I got a Plan B. My period is late by 7 days. Is this from taking the Plan B? When I took one with my ex my period was late but only by a few days.