Hello, I really appreciate your concern. A brown vaginal discharge instead of a period usually occurs due to late periods itself. In majority instances, a brown discharge is just the remains of a delayed period. In many cases, hormonal imbalance due to polycystic disease or other causes may be the reason for discharge that occurs instead of periods. Large amount of brown discharge with unpleasant smell may be due to sexually transmitted infection of the reproductive tract, pelvic inflammatory disease or cancer of cervix. If you are having foul smelling brown discharge then you should consult your physician for further management. Hope my answer has solved your query. Take Care. Thank you.