Quoting Vanilla MILFshake.:" Plan B can cause changes in your cycle or spotting like that. I believe it even says all that in the little booklet that comes in the box with it. I never had issues like that when I took it though."
Quoting RyanKarlie:" I don't think I should be due for a period for another two weeks. But I just had my son and one PP period so far. So my 30 day cycle could have changed."
Quoting Vanilla MILFshake.:" I'd just give it about 2 weeks from the day you had sex and take a test. If the first one is negative ... [snip!] ... still haven't got your period, then test again in a few days. It is possible for plan B to throw things off a little though."