Eh, lepas bersalin memang hormones lagi kelirau kan, especially kalau still breastfeeding, a few of my mum friends juga delayed periods for months even with protection sebab lactation hormones masih kat dalam badan. Since your UPT was negative 3 days ago tapi period still tak datang, honestly safest move is check dengan doctor cepat je, just to be sure and get your mind at ease, they can do a proper test or check if your cycle just belum settle lagi from the pregnancy hormones. Don't stress yourself terlalu much though; it's super common postpartum!