What Causes Irregularities In Periods?

i'm 23 yrs.female,unmarried.i had PCOS.my docter suggested 'Tarana(contraceptive)and glyciphage for 1year.after one year i visited my docter once again,she told that to stop the Tarana,and will continue the Glyciphage till my marriage.my periods not regular yet.i miss my this month period,i have one more problem,i.e,nowadays my breast produces milk, only when i squeeze it.i'm getting afraid.please help me.