I was having irregular periods since last 6 months , I went to a gynecologist last month she prescribed to have birth control pills which I had to start taking from my first day of periods for 21 days  and then had to take a break of 7 days then restart the cycle. My 7 days are over but my periods of this month had not started . Should I start taking the pills or should I wait for my periods to start .Please advice.