Two important possibilities are uterine adhesions and endometriosis. Other causes for such hypomenorrhea which need to be evaluated include hormonal imbalance like low thyroid hormone level and high prolactin, insulin or androgen levels, anxiety and stress, overexercising, malnutrition, anorexia, thyroid disease, polycystic ovarian disease and diseases of the hypothalamus or pituitary...I would suggest you to consult nearest gynecologists for clinical examination and for relevant investigations they will do the needful..