In the past maybe five months i haven't got my period. why?

Amenorrhea: Start with a pregnancy test. If preg test negative other possibilities include: low body weight, medications like birth control pills or depoprovera injection, hormone imbalances (either ovary or brain causing).

Further eval: If you are not pregnant, you need to get additional blood work to check for hormone imbalance. Examples include thyroid hormone and prolactin. See an endocrinologist or your primary care.