Gastroenteritis: This is a common condition that can cause right lower quadrant pain and diarrhea due to inflammation of the gastrointestinal tract, often caused by viral or bacterial infections.

Appendicitis: Although classically presenting with pain migrating to the right lower quadrant, some cases may start with diarrhea, making it a plausible diagnosis.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic diarrhea and abdominal pain, including in the right lower quadrant.
Diverticulitis: Inflammation of a diverticulum in the colon can cause pain, often in the left lower quadrant but can occasionally be in the right lower quadrant, and may be accompanied by changes in bowel habits like diarrhea.

Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause severe abdominal pain, diarrhea, and potentially lead to bowel obstruction or ischemia if not promptly treated.
Ectopic Pregnancy: Although more commonly associated with pelvic pain, an ectopic pregnancy can cause abdominal pain that might be perceived in the right lower quadrant and can be accompanied by gastrointestinal symptoms due to the proximity of the reproductive organs to the intestines.
Mesenteric Lymphadenitis: Inflammation of the lymph nodes in the mesentery can mimic appendicitis and cause significant pain and gastrointestinal symptoms.

Meckel's Diverticulitis: Inflammation of a Meckel's diverticulum, a congenital anomaly of the small intestine, can cause right lower quadrant pain and gastrointestinal symptoms.
Carcinoid Tumor: A rare tumor of the neuroendocrine system that can cause abdominal pain, diarrhea, and other systemic symptoms due to the secretion of various hormones.
Yersiniosis: A bacterial infection caused by Yersinia enterocolitica, which can lead to abdominal pain, diarrhea, and occasionally mimic appendicitis.