What Causes A Delay In Periods Despite Medications?

hello there..I'm 23 years old female...I hv been diagnosed with PCOD in 2007 and was prescribed to take Krimson-35 tab daily atleast fr an year after..after an year I stopped it and after some 5-6 months the problem recurred and I didn't get my periods..I was given Primolut-N and within 7-8 days I got my periods with pain..Again I started with krimson-35 and held onto it for 2 years later with 1-2 months skipping in between but was otherwise regularly taking it..This year in march I was again asked to stop krimson-35 and go with an Ayurvedic syrup 'Amycordial' twice a day..but to despair this month i hvnt got my periods..they were supposed to come on/near 15th june. The doctor gave me sysron-n beg from 22nd june to bring the periods but till now hvnt got them...plz tell me h could be the other prb ths time...