Ahhh I understand why you're worried lah, any spotting masa pregnant memang bikin jantung lompat! Tapi kadang-kadang it's just urine residue or discharge yang kena oxidize on the pad jadi nampak coklat je, especially kalau not fresh. Tapi since you're at 21 weeks, I think best to give your gynae a quick call atau WhatsApp la, just to be safe and dapat peace of mind, a few of us had similar scares and our doctors checked us super cepat je, so jangan hesitate. Better to check than worry alone, kan? How are you feeling otherwise, any cramps or other symptoms?