Cramping, nausea, and no period after plan b?

I took plan b on saturday (about 12 hours after i had and the condom broke), and it's now monday and i'm nauseous and have cramps like i'm going to start my period. I haven't had any bleeding at all and that worries me because i've read that most women bleed after taking plan b. I'm also steadily on birth control but freaked out when the condom broke. Could i be pregnant or what's going on here?