Firstly you should always take a pregnancy test 3 weeks after taking an emergency contraceptive pill to ensure it worked.
As you’re on the pill, you don’t have a real natural cycle or period, so any bleeding you experience is just a side effect of the pill and not an actual period. It is totally normal for bleeds on the pill to be slightly different, you’re not going to start bleeding at exactly the same time every single month. Missed bleeds and irregular bleeds are normal side effects of the pill. Missing pills can sometimes lead to experiencing side effects on the pill, including irregular bleeding.
However, irregular bleeding/periods are a common side effect of plan b (see its pamphlet a list of other potential side effects) so yes it potentially could be from that.
