A 7-day-old female infant born to a 28-year-old primigravida mother presents with poor feeding, excessive crying, and weight loss of 12% from birth weight. On examination, the infant appears jaundiced (bilirubin 18 mg/dL). The mother reports that breastfeeding sessions last only 5–10 minutes, the infant seems unsatisfied, and she has not heard swallowing sounds. Breast examination reveals engorged, tense breasts with a flat nipple. The infant's latch appears shallow with only the nipple in the mouth. What is the most likely diagnosis?