Definition: The failure to menstruate for at least 6 months during the reproductive years – in absence of pregnancy ( some authors require only 3 months).
1) Primary: it is the failure to menstruate by the age of 16 or later; i.e.: delayed ménage
2) Secondary: it is the absence of menses when previously it occurred; i.e.: postmenarchal amenorrhea.
This disorder needs to be evaluated by your gynaecologist.