Mama, please go to your doctor or clinic agad-agad para ma-check yan, abdominal pain with that heaviness, lalo na ngayon lang lumalabas, needs proper assessment. Hindi kami dapat mag-assume, okay?
A few of us mums experienced similar after delivery, but each case is different talaga, so better safe than sorry. Your doc can really rule out what's happening, could be lots of things, from normal postpartum stuff to something that needs attention. Don't delay, ha? Especially since you're breastfeeding, you need to be 100% well.