is stress delaying my period?

So almost six weeks ago, my boyfriend and I were having sex and we didn't notice when the condom fell off. He came inside me, so the next morning (less than 12 hours later), we got plan b. Less than a week later, I started my period, and I was due to start a few days before it did actually, but I get that plan b messes with your cycle. I also know that I was "infertile" because I was just at that phase of the cycle. Now, I'm 6 days late on my next period and of course I'm freaking out. The odds should be on my side, but could I still be pregnant, or am I just stressing and causing an even greater delay? Could this also be because of the plan b?