Hello, First of all, you need to undergo one blood test for beta-HCG and TVS scan to rule out pregnancy at the earliest. Early pregnancy test may give negative result. In exclusion of pregnancy, other reasons are hormonal imbalance, thyroid disturbance, vaginal or pelvic infection, ovarian cyst, stress/ anxiety, over wt or loss, irregular diet habit etc. Please consult with gynecologist following test reports to proceed other relevant investigations to pin point the diagnosis. Take suggestive measures accordingly. Try to avoid stress/ anxiety, take healthy diet with iron supplements, drink plenty of water, maintain genital hygiene and take sound sleep. Good luck.