Plan B can really mess up your cycle. It did with mine when I took it before. I think you are okay because by now a pregnancy would have shown up posotive if you haven't had unprotected sex since you took the pill!
Most girls who take plan B have irregular periods and bleeding after due to the hormones in it. That's common and normal. I'm sure some have not had the plan b work but in general, it's pretty effective. I doubt you are pregnant from what you describe. good luck