Ay alam ko yan worry mo, lalo na walang period pa! Honestly, brown discharge kaya mabilis maubos especially with mixed feeding, minsan ang body ay unpredictable pa sa postpartum, pero since you had unprotected sex, best talaga na magpa-test ka na lang ng pregnancy test or mag-check sa doctor para sure, kasi parang ang timeline ay possible for implantation bleeding talaga, and you're right na pwedeng mabuntis kahit walang period pa dahil sa breastfeeding. A few of us mums din experienced spotting postpartum na hindi pregnancy, pero after unprotected sex better safe than sorry na lang talaga! Get yourself tested soon para peace of mind mo, sana negative lang and regular cycle mo na umuusad!