plan b

Nancy
Okay I am freaking out, I ran out of bc so I stopped taking it. The day I was suppose to start a new pack I had u protected sex and didn't think to take plan b. Throughout the month I had unprotected sex again and took a plan b, I am three days late today. Could it from the plan b ? I took a pregnancy test on the day my period was due and it was negative. Should I be worried!?