Irregular and infrequent menstruation is known as:

Oligomenorrhoea - Infrequent and irregularly timed episodes of bleeding usually occuring at intervals of more than 35 days Polymenorrhoea - Frequent episodes of mentruation usually occurring at intervals of 21 days or less Menorrhagia - Increased menstrual flow/Increased duration at regular cycles Hypomenorrhoea - Scanty bleeding and shoer days of bleeding Metrorrhagia - Irregular bleeding in between the cycles Menometrorrhagia - Increased menstrual flow as well as irregular bleeding between the cycles