Constipation: This is the most likely diagnosis because feeling stool in the left lower quadrant is a common symptom of constipation, where stool accumulates in the sigmoid colon, which is located in the left lower quadrant of the abdomen.

Diverticulitis: Inflammation of the diverticula in the sigmoid colon can cause pain and sensation of stool in the left lower quadrant.
Irritable Bowel Syndrome (IBS): IBS can cause a variety of symptoms including abdominal pain, changes in bowel habits, and sensation of stool in the left lower quadrant.
Sigmoid Volvulus: A twisting of the sigmoid colon can cause an obstruction, leading to a sensation of stool in the left lower quadrant.

Intestinal Obstruction: A blockage in the intestine can cause severe abdominal pain, vomiting, and a sensation of stool in the left lower quadrant. This is a medical emergency.
Appendicitis (atypical presentation): Although appendicitis typically presents with pain in the right lower quadrant, in some cases, especially if the appendix is retrocecal, the pain can be felt in the left lower quadrant.
Colorectal Cancer: A tumor in the sigmoid colon can cause a sensation of stool in the left lower quadrant, along with other symptoms such as changes in bowel habits, weight loss, and blood in the stool.

Intussusception: A condition where a part of the intestine telescopes into another part, which can cause abdominal pain and a sensation of stool in the left lower quadrant.
Ovarian Torsion: In females, a twisting of the ovary can cause severe abdominal pain, which can sometimes be referred to the left lower quadrant.
Inflammatory Bowel Disease (e.g., Crohn's Disease, Ulcerative Colitis): These conditions can cause chronic inflammation of the gastrointestinal tract, leading to a variety of symptoms including abdominal pain and changes in bowel habits.