Firstly have u lost ur weight or gain ur weight that also sometimes leads to hypomenorrhea....secondly if not then it may be due to hormonal imbalance....can be thyroid, prolactin level, PCOS.....thirdly stress if ur taking to much of stress that also contribute in irregularity in ur periods... fourth r u on OCP pill or not ......so go for investigation if they r normal then periods can be regular by hormonal medicines( oestrogen and progesterone) for 3 to 6 month

Detailed evaluation required.

Hi U need complete evaluation.  Their are many things , thyroid , prolactin , any weight gain or weight loss , any chronic medicines alm wil affect periods 

U need consultation with gynecologist