Hello, First of all, you need to undergo one blood test for beta-hCG and TVS scan at the earliest to rule out conception or pelvic pathology. In exclusion of pregnancy, other reasons are hormonal imbalance (effect of the pill), mental stress/ depression, ovarian cyst, hypothyroid state, over wt/ loss, irregular diet habit, pelvic/ vaginal infection etc. Following initial test reports, you need to consult with your gynecologist to proceed other relevant investigation like pelvic USG, hormone assay, prolactin level etc. Take proper medication according to etiology. Take healthy diet with iron supplement, control body wt, avoid stress, maintain genital hygiene and take sound sleep. Good luck.