Gastroesophageal Reflux (GER): This is the most common cause of non-bilious vomiting in infants, especially at this age. The stable weight gain and normal physical exam support this diagnosis, as most infants with GER continue to gain weight appropriately despite frequent vomiting.

Overfeeding or Incorrect Feeding Technique: Overfeeding or using an inappropriate feeding technique can lead to non-bilious vomiting. This is common in bottle-fed infants but can also occur in breastfed babies.
Infection (e.g., Urinary Tract Infection): Although less common, infections such as urinary tract infections can cause vomiting in infants. The absence of other symptoms does not rule out this possibility.
Food Allergy or Intolerance: Allergies to milk proteins or other components of formula can cause vomiting. This is more likely in formula-fed infants but can also occur in breastfed infants if the mother consumes allergenic foods.

Pyloric Stenosis: Although typically presents with bilious vomiting, in early stages, it might not be bilious. It's crucial to monitor for signs of dehydration and ensure the vomiting does not become bilious, which would necessitate urgent surgical evaluation.
Inborn Errors of Metabolism: Certain metabolic disorders can present with vomiting. While rare, these conditions can be life-threatening if not identified and treated promptly.
Congenital Anomalies (e.g., Esophageal Atresia, Tracheoesophageal Fistula): These conditions are usually identified shortly after birth but can occasionally present later with non-bilious vomiting if there's a partial obstruction.

Eosinophilic Esophagitis: An allergic inflammatory condition of the esophagus that can cause vomiting, though it's more commonly associated with feeding difficulties and failure to thrive in older infants.
Gastrointestinal Obstruction: Conditions like intestinal malrotation or Hirschsprung's disease can cause vomiting, though they typically present with other symptoms such as abdominal distension or failure to pass meconium.
Neurological Conditions (e.g., Increased Intracranial Pressure): Rarely, neurological conditions can cause vomiting in infants. These would typically be accompanied by other neurological signs or symptoms.