Hello..my Period Starts On Every 28th Day.but Stopped On 4th

Hello..my period starts on every 28th day.but stopped on 4th day of the cycle and again started on 5th day with pain in my lower abdomen.so i consulted with doctor.and she gave me orgatril.she said to start orgatril from 16th day of my cycle and to continue for 10day.i started it last month.this month my period started on 15th march And ends at 21st march.bt my period started again today in 14th day.i dont know what is the problem.should i take orgatril like before on 16th day from my previous cycle?