Gastroenteritis: This is often the most common cause of vomiting that lasts for a week, typically caused by a viral or bacterial infection leading to inflammation of the stomach and intestines.

Food poisoning: Similar to gastroenteritis, food poisoning can cause prolonged vomiting due to the consumption of contaminated food.
Viral gastroenteritis (e.g., norovirus): Highly contagious and can lead to severe vomiting.
Gastritis: Inflammation of the stomach lining, which can be caused by infection, medication, or other factors.
Peptic ulcer disease: Ulcers in the stomach or duodenum can cause vomiting, especially if they bleed or perforate.

Appendicitis: Although vomiting is not the primary symptom, it can occur, especially if the appendix ruptures, making it a critical diagnosis not to miss.
Intestinal obstruction: A blockage in the intestines can cause severe vomiting and is a medical emergency.
Pancreatitis: Inflammation of the pancreas can cause vomiting and is a serious condition requiring prompt treatment.
Diabetic ketoacidosis: A complication of diabetes that can cause vomiting among other severe symptoms.

Brain tumors or cysts: Rarely, increased intracranial pressure from a brain tumor or cyst can cause vomiting.
Addison's disease: A rare disorder of the adrenal glands that can lead to vomiting among other symptoms.
Porphyrias: A group of rare genetic disorders that can cause abdominal pain, vomiting, and other neurological symptoms.
Superior mesenteric artery syndrome: A rare condition where the duodenum is compressed, leading to vomiting and other gastrointestinal symptoms.