My boyfriend and I had sex on a Sunday, the same day my period ended. My cycles usually fluctuate but on average are pretty long (around 32-36 days) and I bleed for 6/7 days. 

The condom we used didn't break, but we noticed fresh stains on the sheet that I wasn't sure was either me or due to how he took the condom off. He was sure nothing got inside me but I took plan b approximately 72 hours later just to be safe. 

About 5 days later, I had slight cramps and spotting which turned into what was a regular period for me. Flow was the same, I passed a lot of clots (normal for me) which I assumed to be my uterus lining as usual, and it lasted about 5 days, just a little shorter than my regular period. 

Now, my period is quite late if you count from the time of my actual period, but isn't late at all if counting from the plan-b induced period. 

I've also taken 4 at home pregnancy tests every week since 2 weeks after the day we had sex (all negative) and 2 urine tests in a clinic which also came back negative. The most recent one was about 3 days ago in a clinic and 5 days ago at home. 

At this point, I would be 6 weeks along if I was pregnant and I have no symptoms of pregnancy besides headaches which I believe may be due to stress, because of university. I also experienced slight cramping, like I usually get before my period is about to start, a couple of times in the  past few days but it hasn't. 

I know it probably sounds crazy but you always hear about these freak accidents/stories about how some  people get pregnant I can't help but worry... should I be concerned? Should I count my plan b period as my period and count from there? Can plan b reset your cycle?