Appendicitis: This is often the first consideration for lower abdominal pain, especially if the pain is localized to the right lower quadrant. The classic presentation includes initial diffuse or periumbilical pain that migrates to the right lower quadrant, accompanied by fever, nausea, and vomiting.

Urinary Tract Infection (UTI): Lower abdominal pain can be a symptom of a UTI, particularly if the infection has ascended to the kidneys (pyelonephritis). Symptoms may include dysuria, frequency, urgency, and flank pain.
Ovarian Cyst: Ovarian cysts can cause lower abdominal pain, especially if they rupture or twist (torsion). The pain is often sharp and can be accompanied by nausea and vomiting.
Diverticulitis: Inflammation of a diverticulum in the colon can cause lower abdominal pain, usually on the left side, along with changes in bowel habits, fever, and possible nausea and vomiting.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic lower abdominal pain, diarrhea, weight loss, and sometimes blood in the stool.

Ectopic Pregnancy: Although less common, an ectopic pregnancy is a life-threatening condition that must be considered, especially in women of childbearing age presenting with lower abdominal pain and a missed period or positive pregnancy test.
Ruptured Aneurysm: A ruptured abdominal aortic aneurysm can cause severe, sudden lower abdominal pain and is a medical emergency.
Intestinal Obstruction: This condition, where part of the intestine is blocked, can cause severe abdominal pain, vomiting, and constipation. It requires immediate medical attention.
Pulmonary Embolism: While the primary symptom is chest pain, a pulmonary embolism can sometimes refer pain to the lower abdomen, especially if the embolism is large.

Endometriosis: While not rare, endometriosis can cause chronic lower abdominal pain, especially during menstruation. It's less likely to be considered initially without a history of similar cyclic pain.
Lymphoma: Abdominal lymphoma can cause lower abdominal pain, usually as part of a broader symptom complex including weight loss, fever, and night sweats.
Tuberculosis: Abdominal tuberculosis can cause chronic lower abdominal pain, weight loss, and changes in bowel habits, but it is relatively rare in many parts of the world.
Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodic abdominal pain, hypertension, and other symptoms like palpitations and sweating.