What Causes Delay In Periods?

I has sex the day my period ended(May 1-6th), the condom broke so i took plan b the next morning. then 5 days later i was bleeding-seems like a short period. then i had sex with my bf after that but using condoms. I am suppose to be expecting my period around June 1st but it's already June 11th. I took a pregnancy test in the afternoon on June 9th and it was negative. Should i be worried? i don't know what to do.