I have an irregular period i haven't got it in 3 months had unprotected sex and took plan b and got period a week after should i be worried?

Irregular periods: Causes of irregular period include anovulatory cycle, obesity, thyroid issues, hormonal imbalance. Because your period has been irregular, the Plan B could have provide a surge of extra surge of Progesterone hormone to cause bleeding. First you should get a pregnancy and keep a menstrual diary that you can take to see your doctor. Good health.