Period after Plan B

My boyfriend and I had some close to unprotected sex the weekend of November 6-7. I took plan b in the evening on November 7 and started having some red and then brown discharge on November 13th. It turned into what I assumed was a full period that lasted over 7 days because one day I bled so hard it went through my slacks at work. My current period for this month is a week late according to the app. I’ve had some stress and sickness (sinus crud this weekend) over the last few weeks. Is my delay due to the plan b or is it because of the sickness? Should I be worried?