Appendicitis: This is often the first consideration for right lower abdominal pain, especially if the pain is severe, constant, and accompanied by fever, nausea, and vomiting. The pain typically starts near the navel and then moves to the right lower abdomen.

Ovarian Cyst or Torsion: In females, ovarian cysts can cause right lower abdominal pain if they rupture or become twisted, cutting off their blood supply. Symptoms can include sudden, severe pain, and sometimes nausea and vomiting.
Kidney Stone: A stone in the right ureter can cause severe, crampy pain in the right lower abdomen that may radiate to the groin. It's often accompanied by nausea, vomiting, and sometimes blood in the urine.
Diverticulitis: Inflammation of a diverticulum in the right colon can cause pain in the right lower abdomen, fever, nausea, and changes in bowel habits.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic inflammation of the gastrointestinal tract, leading to abdominal pain, diarrhea, weight loss, and sometimes blood in the stool.

Ectopic Pregnancy: Although less common, an ectopic pregnancy can present with lower abdominal pain, especially if the ectopic pregnancy is located in the right fallopian tube. It's a medical emergency if the ectopic pregnancy ruptures.
Ruptured Aneurysm: A ruptured abdominal aortic aneurysm can cause severe abdominal pain that may radiate to the back, but it's less common for the pain to be localized to the right lower abdomen. However, it's a life-threatening condition that requires immediate attention.
Intussusception: This condition, where a part of the intestine slides into an adjacent part, can cause severe abdominal pain, vomiting, and sometimes bloody stools. It's more common in children but can occur in adults.

Mesenteric Lymphadenitis: Inflammation of the lymph nodes in the mesentery (the tissue that attaches the intestines to the back of the abdominal wall) can mimic appendicitis but is less common.
Right Lower Lobe Pneumonia: Sometimes, pneumonia in the right lower lobe of the lung can cause referred pain to the right lower abdomen, especially if the inflammation irritates the diaphragm.
Endometriosis: Although not typically an acute presentation, endometriosis can cause chronic right lower abdominal pain in females, especially during menstruation, if endometrial tissue is present in the right lower abdomen.