Ay hirap talaga yan, sis! Brown spotting parang irregular lang siya usually, pero since ang last period mo was Dec 9 at negative ang PT mo on Jan 24, mas maganda pang mag-PT ulit after a few days or better, mag-consult na sa doctor para sure, kasi kung may possibility talaga ng pregnancy, they can check via ultrasound na or blood test which mas accurate. A few of us din went through ganito and turned out delayed lang or hormonal imbalance, pero best peace of mind talaga is makakuha ng professional opinion na. Don't worry, maraming possible reasons ito, so hintayin mo nalang ang next test or go see your OB na para di ka mag-worry pa.