Ah sis, totally normal yan! A few of us had irregular periods for months after giving birth, especially if breastfeeding ka pa, the hormones are still all over the place talaga. Since negative ang PT mo, hindi ka pregnant, so most likely it's just your body adjusting pa lang; mine took like 6 months before it settled into a regular cycle ulit, kaya don't stress too much about 3 days delay pa lang.