There are several reasons for missing your period that long, this may include diseases of the ovaries, like the polycystic disease, it may well be diseases of glands like the thyroid and the pituitary, in addition; premarure failure of the ovaries although no common but may happen.without complete investigations, it would be difficult to know the cause, some coild like the Mirena IUS ( the hormonal cpoil) may cause the period to disappear in around 20% of women, but i think you should be thoroughly evaluated before we decide the cause and the treatment. Regards