In this circumstance, I suggest you to undergo one blood test
for beta-hCG and TVS scan to rule out possible conception. Brown discharge is commonly associated with implantation
bleeding or early sign of miscarriage
Other reasons are vaginal or pelvic infection
, old endometrial tissue with clots, hormonal imbalance etc.
Please consult with your gynecologist following above test reports. Maintain genital hygiene properly. Good luck.