A 4-week-old infant presents to clinic for a well child check. This infant had an uneventful delivery by NSVD at full term and subsequent normal neonatal screen. The nurse reports that her growth is a concern, with weight at 3.0 kg (< 3rd percentile) and weight for height at < 3rd percentile. Mom denies any drinking or drugs since before this pregnancy and says she has been breastfeeding every two to three hours and supplementing with appropriately mixed formula one to two times a day. She does report the baby seems to have issues latching and some possible gasping between suckles. There has been no diarrhea, hematochezia, vomiting, or fevers. The vital signs and exam (apart from a thin infant) are normal. The mother's affect is flat, and she seems anxious when you ask her about her infant. What is the most likely diagnosis for this infant's failure to thrive