Took plan b, had a heavy period then next 2 periods have been light, all pregnancy tests say negative. plan b side effects??

Likely side effect: Hello , When you take the morning after pill, Plan B or Levonorgestrel for emergency contraception,. remember that you are taking a hormone. Since the menstrual period is a hormonal system, the onset and quality of the menses will be effected. Expect your period to be delayed and the menses to be somewhat heavier. You can expect to return to normal cycles soon.