What Causes Two Periods In One Month?

i am lakshmi 26yrs old. I have got married in Feb 2012. I have missed periods and also cyst in ovaries. i didnt get periods regularly eventhough used tablets. in 2014 femilon tablet used for regular periods for 3months. Now i have regular periods but twice in a month, at that time i used ovabless tablet. and there is no cyst in ovary. Now i stop using ovabless tablet. what is the reason for periods two times in a month?