Gastroesophageal Reflux (GER): This is a common condition in newborns where stomach acid flows back into the esophagus, causing vomiting and nausea. It's often due to an immature lower esophageal sphincter.

Infectious Gastroenteritis: Viral or bacterial infections can cause inflammation of the stomach and intestines, leading to vomiting and nausea in newborns.
Pyloric Stenosis: A condition where the pylorus (the passage between the stomach and small intestine) is narrowed, causing projectile vomiting.
Overfeeding or Underfeeding: Incorrect feeding techniques or amounts can lead to vomiting and nausea in newborns.

Intestinal Obstruction: A blockage in the intestines can cause severe vomiting and nausea, and if missed, can lead to serious complications, including death.
Congenital Diaphragmatic Hernia: A birth defect where the diaphragm doesn't form properly, allowing abdominal organs to move into the chest cavity, which can cause vomiting and nausea.
Necrotizing Enterocolitis: A condition where a portion of the bowel dies, often due to a lack of blood supply, which can cause severe vomiting and nausea.

Congenital Hypertrophic Pyloric Stenosis: A rare condition where the pylorus is thickened, causing narrowing of the passage between the stomach and small intestine.
Gastroschisis: A rare birth defect where the baby's intestines protrude through a hole in the abdominal wall, which can cause vomiting and nausea.
Hirschsprung's Disease: A rare condition where nerves are missing from parts of the bowel, causing severe constipation or intestinal obstruction, which can lead to vomiting and nausea.