Gastroenteritis: This is often the most common cause of stomach pain and intestinal inflammation, typically resulting from viral or bacterial infections, and sometimes from parasites or other pathogens. The symptoms can range from mild to severe and include diarrhea, vomiting, and abdominal cramps.

Irritable Bowel Syndrome (IBS): Characterized by chronic abdominal pain, bloating, and alteration of bowel habits in the absence of any mechanical, inflammatory, or biochemical abnormalities. It's a common condition that can cause significant discomfort and affect quality of life.
Inflammatory Bowel Disease (IBD): This includes conditions like Crohn's disease and ulcerative colitis, which are characterized by chronic inflammation of the gastrointestinal tract. Symptoms can include persistent diarrhea, abdominal pain, rectal bleeding, weight loss, and fatigue.
Peptic Ulcer Disease: This condition involves sores in the lining of the stomach or the first part of the small intestine, leading to pain and inflammation. The pain is often described as a gnawing or burning sensation in the upper abdomen.

Appendicitis: Although it primarily causes pain in the lower right abdomen, appendicitis can sometimes present with more generalized abdominal pain and should always be considered in cases of acute abdominal pain due to its potential for serious complications if not promptly treated.
Intestinal Obstruction: This is a blockage that prevents the normal flow of the products of digestion, including food, fluid, and gas. It can cause severe abdominal pain, vomiting, and constipation, and requires immediate medical attention.
Mesenteric Ischemia: A condition where there's a blockage in one of the arteries that supply blood to the intestine, leading to tissue death. It's a medical emergency that presents with severe abdominal pain out of proportion to the physical examination.

Eosinophilic Gastroenteritis: A rare condition characterized by the presence of eosinophils in the gastrointestinal tract, leading to inflammation and symptoms like abdominal pain, nausea, vomiting, and diarrhea.
Whipple's Disease: A rare, systemic bacterial infection caused by Tropheryma whipplei, which can lead to malabsorption, weight loss, diarrhea, and abdominal pain, among other symptoms.
Behçet's Disease: A form of vasculitis that can affect various parts of the body, including the gastrointestinal tract, leading to symptoms like abdominal pain, diarrhea, and intestinal inflammation.