Irritable Bowel Syndrome (IBS): This condition is characterized by chronic abdominal pain, bloating, and alteration of bowel habits in the absence of any mechanical, inflammatory, or biochemical abnormalities. The patient's symptoms of blood spotting in stool, mucus in stool, and the need to defecate after every meal, without extreme stomach pain or tiredness, align closely with IBS, particularly the subtype IBS-D (diarrhea-predominant).

Inflammatory Bowel Disease (IBD): Conditions like Ulcerative Colitis (UC) and Crohn's Disease (CD) can present with similar symptoms, including blood and mucus in the stool. However, they typically are associated with more significant pain and systemic symptoms like weight loss and fatigue, which this patient does not exhibit.
Gastroesophageal Reflux Disease (GERD): Although primarily associated with heartburn and regurgitation, some patients with GERD may experience diarrhea or urgent bowel movements, possibly due to the reflux of stomach contents into the small intestine.
Infectious Gastroenteritis: Chronic or recurrent infections could lead to persistent gastrointestinal symptoms. However, the lack of systemic symptoms like fever or significant abdominal pain makes this less likely.

Colorectal Cancer: Although rare in young adults, colorectal cancer can present with rectal bleeding and changes in bowel habits. It's crucial to rule out this diagnosis, especially if there's a family history.
Inflammatory Bowel Disease Complications: If the patient has undiagnosed IBD, complications like strictures, fistulas, or toxic megacolon could be life-threatening and require immediate attention.
Gastrointestinal Lymphoma: A rare condition that could present with chronic gastrointestinal symptoms, including diarrhea and abdominal pain.

Microscopic Colitis: A condition characterized by chronic, watery diarrhea, often without blood or mucus, and normal colonoscopy findings but with microscopic evidence of inflammation.
Eosinophilic Gastroenteritis: A rare condition involving eosinophilic infiltration of the gastrointestinal tract, which can cause a variety of symptoms including diarrhea, abdominal pain, and sometimes blood in the stool.
Whipple's Disease: A rare, systemic bacterial infection that can cause malabsorption, weight loss, diarrhea, and abdominal pain, although it typically presents with more systemic symptoms.