HELP! Could I be pregnant?

I was with my boyfriend may 19, and we didnt use any protection. 12 hours later i took the Plan B pill, 5 days later I got my period for about 3 days. Now today I am supposed to get my period and it hasnt came yet. (My boyfriend and I had a week ago and he pulled out.) Could I be pregnant? Or is the Plan B pill from earlier messing up my menstral cycle? Im having really bad cramps today but no bleeding?