Viral Gastroenteritis: This is the most common cause of diarrhea and abdominal pain, often due to norovirus or rotavirus, and is usually self-limiting.

Bacterial Gastroenteritis: Caused by bacteria such as Salmonella, Shigella, or E. coli, which can lead to more severe symptoms and may require antibiotic treatment.
Food Poisoning: Similar to bacterial gastroenteritis but typically related to the consumption of contaminated food.
Irritable Bowel Syndrome (IBS): A chronic condition characterized by recurring abdominal pain and changes in bowel movements, which can include diarrhea.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis, which cause chronic inflammation of the gastrointestinal tract, leading to symptoms including diarrhea and abdominal pain.

Appendicitis: Although less common, appendicitis is a medical emergency that requires prompt surgical intervention. It typically presents with abdominal pain that migrates to the lower right quadrant, and while diarrhea is not a primary symptom, it can occur.
Intussusception: A condition where a part of the intestine slides into an adjacent part, potentially cutting off blood supply. It's more common in children and can cause severe abdominal pain and diarrhea.
Mesenteric Ischemia: A condition where blood flow to the intestines is blocked, leading to tissue death. It's a medical emergency that can present with severe abdominal pain and diarrhea.

Whipple's Disease: A rare, systemic bacterial infection that can cause diarrhea, abdominal pain, and malabsorption.
Giardiasis: An intestinal infection caused by the parasite Giardia lamblia, which can lead to chronic diarrhea and abdominal pain.
Celiac Disease: An autoimmune disorder where the ingestion of gluten leads to damage in the small intestine, causing diarrhea, abdominal pain, and malabsorption.
Microscopic Colitis: A condition characterized by inflammation of the colon, leading to chronic diarrhea and abdominal pain, often without visible signs of inflammation on endoscopy.