Gastroenteritis: This is often the most common cause of umbilical stomach pain, especially in children and young adults. It is usually viral in nature and can be accompanied by symptoms such as diarrhea, vomiting, and fever.

Irritable Bowel Syndrome (IBS): A common condition characterized by abdominal pain, bloating, and changes in bowel movements. The pain is often localized around the umbilicus.
Constipation: Can cause significant abdominal pain, including around the umbilical area, especially if the constipation is severe or chronic.
Gastroesophageal Reflux Disease (GERD): Although more commonly associated with chest pain, GERD can also cause abdominal pain, including around the umbilicus, due to the reflux of stomach contents into the esophagus.

Appendicitis: Although the pain of appendicitis typically starts near the umbilicus and then moves to the lower right abdomen, it's crucial not to miss this diagnosis as appendicitis can lead to severe complications if not treated promptly.
Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause severe abdominal pain, including around the umbilicus, and is a medical emergency.
Volvolus or Intestinal Obstruction: These conditions can cause severe abdominal pain, vomiting, and constipation. They are emergencies that require immediate medical attention.

Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause abdominal pain, including around the umbilicus, especially if it becomes inflamed or infected.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic abdominal pain, including around the umbilicus, along with changes in bowel habits and weight loss.
Abdominal Migraine: A condition that can cause recurrent episodes of abdominal pain, often around the umbilicus, in children, which may be associated with migraine headaches.