Hello, First of all, you should undergo one blood test for beta-HCG and TVS scan to confirm/ exclude pregnancy at the earliest. Some times late period with brown discharge may indicate early sign of miscarriage. In exclusion of pregnancy, other reasons are hormonal imbalance, vaginal infection, stress/ anxiety, thyroid problem, weight gain/ extreme loss, irregular eating habits, psychological factor etc. Need to investigate properly to pin point the diagnosis by complete hormone assay, thyroid profile, blood sugar & prolactin level, vaginal swab test etc. Consult with your gynecologist for proper guidance and medication. Avoid stress/ tension, take healthy diet with Vitamin & iron supplements, control body wt, maintain genital hygiene and take sound sleep. Be well and take care.