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: Resulting from the consumption of contaminated food, which can cause sudden onset of diarrhea and abdominal pain.
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 are chronic and can cause diarrhea, abdominal pain, and other symptoms.

Appendicitis: Although less common, appendicitis can present with abdominal pain and diarrhea, and if missed, can lead to severe complications.
Intussusception: A condition where a part of the intestine slides into another, which can cause severe abdominal pain and diarrhea, especially in children.
Mesenteric Ischemia: A serious condition where the blood flow to the intestines is blocked, which can cause severe abdominal pain and diarrhea.
Diverticulitis: Inflammation of the diverticula in the colon, which can cause abdominal pain and changes in bowel habits.

Celiac Disease: An autoimmune disorder where the ingestion of gluten leads to damage in the small intestine, causing chronic diarrhea and abdominal pain.
Whipple's Disease: A rare bacterial infection that affects the small intestine and can cause diarrhea, abdominal pain, and weight loss.
Giardiasis: An intestinal infection caused by the Giardia parasite, which can lead to chronic diarrhea and abdominal pain.
Lactose Intolerance: The inability to digest lactose, leading to bloating, gas, diarrhea, and abdominal pain after consuming lactose-containing products.