​A 3-day-old, full-term male infant is brought to the clinic by his parents due to yellowish discoloration of his skin and eyes. He was born via normal spontaneous vaginal delivery with no complications and was exclusively breastfed. The parents report he has been feeding well, having regular wet diapers, and passing meconium. On examination, the infant is active and alert. His skin appears diffusely icteric down to his abdomen. His vital signs are stable.

Laboratory results show:

Total Bilirubin: 18 mg/dL

Direct Bilirubin: 0.8 mg/dL

Hemoglobin: 16 g/dL

Reticulocyte count: 1.5%

Which of the following is the most likely diagnosis?