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The symptoms presented are classic for pyloric stenosis, particularly in a 6-week-old newborn. Projectile vomiting is a hallmark symptom, typically occurring shortly after feeding. This vomiting is due to the hypertrophy of the pyloric muscle, which obstructs the passage of food from the stomach into the duodenum.

Failure to thrive further supports this diagnosis, as the obstruction leads to inadequate nutritional intake and can result in dehydration and electrolyte imbalances, causing weight loss or insufficient weight gain.

Additionally, the presence of an "olive-like" mass in the abdomen is very characteristic of pyloric stenosis. This mass is palpated just to the right of the midline in the epigastric region, where the enlarged pylorus is located.

In contrast, duodenal atresia typically presents with bilious vomiting shortly after birth and may also be associated with a "double bubble" appearance on radiologic imaging. Gastroesophageal reflux can cause vomiting in infants but doesn't typically present with projectile vomiting or an olive-like mass. Hirschsprung's disease usually affects older infants and children, presenting with constipation and abdominal distention rather than projectile vomiting.

Overall, the combination of symptoms clearly aligns with pyloric stenosis, making it the