What Causes Irregularities In Periods?

Hi Doctor,My name is priya.I had my last periods jan 4th.I did not get my periods last month.This month i visited a gynaecologist and she told to take regestrone tablet.I completed the tablet on 9th but still i did not get my periods.I do have irregular periods some times i.e during my schooldays.I did not have any sexual intercourse.My marriage is next month 26th.How can get my periods?.I had lot of papaya and pineapple juices but no use.Kindly advice me.