I've never taken plan b but it can mess ur period up, not just one cycle but it can mess up several cycles. It may take a few months to get them back to normal, everyone is different.
I believe that the same thing is happening to me as well, I am expecting for my period to come, but no signs of it yet either...
Well my period ended up being 2 months late, which has never happened to me! so my cycle has been regular since. Just take a test or wait it out