What Is The Reason To Miss Periods After Stopping Diane35?

im 36 years old.and im using diane 35 for 5 years.im always regular in my periods.but now after i finish the pack off diane im suppose to have my period during the 7 days break of pill,usually my period comes in 3-4 days,during the 7 days break.but now im 5 days delayed and this is the first time for me.i had a hpt this morning and its negative.plase tell me why it happen.the pills is suppose to regulate my period.