What Causes Missed Period While Having Small Ovarian Cyst?

Hi, I have had a little irregularity with my period. Till 9th December 2013, all was well. I got my period on 9th December 2013, and then again on 25th December 2013. Then the next period came on 1st February 2014, but bleeding was less and then till now I have not got my periods (8th March 2014). Today I visited a gynecologist. She asked me to go for thyroid test and ultrasound. My thyroid report is normal and in ultrasound, it shows there is a small cyst but doctor said it is very small and nothing to worry. She asked me to take meprate tablet for 5 days and to see her again when periods come on the 1st or 2nd day of periods. I am scared. Please help.