What Could Cause Missed Periods After Stopping Duphaston?

Hello! I stopped taking birth contol pills in the autumn and my menstrual cycle turned irregular. Since I had my last periods in November the doctor prescribed me Duphaston 10 mg once a day. I stopped taking Duphaston on this Monday when I had taken 12 tablets. I am a bit worried because the doctor said that the periods will start when I stop taking Duphaston. Should I be worried or should I wait more? Thank you for your answer.