A child was born from the first pregnancy, accompanied by gestosis of the first and second half. The delivery was via a cesarean section. Apgar score - 6 points. The baby's weight - 3000 g. The baby was suckling actively, no burping. Two weeks later, the baby developed projectile vomiting with curdled milk in the vomitus that exceeded in volume the amount of baby's meals. The baby has become lethargic, is poorly gaining weight, the amount of urine and feces has decreased. What is the most likely diagnosis in this case?