I am a 21 year old female and I generally have a very regular and consistent period cycle. For the past two months I took one plan b pill each month.(please note this was my first time using any hormonal contraceptive) I got my period on time for those two months however for the next month my period has been delayed by 9 days. I have had no intercourse or pills this cycle whatsoever. What is causing this delay. I am starting to get worries because my period is very regular and this is the longest it has been delayed.