Irritable Bowel Syndrome (IBS): Given the symptoms of abdominal pain, fatigue, and diarrhea without blood or fever, IBS is a common condition that fits this presentation. The absence of systemic symptoms like fever and the nature of the diarrhea (normal color, no blood) also point towards a functional gastrointestinal disorder.

Infectious Gastroenteritis: Although the patient reports no fever, viral gastroenteritis can present with diarrhea, abdominal pain, and fatigue without fever. The high frequency of diarrhea suggests an infectious cause.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can present with chronic diarrhea, abdominal pain, and fatigue. The absence of blood in the stool does not rule out IBD, as some patients may not have bloody stools, especially in the early stages.
Lactose Intolerance or Other Food Intolerances: These conditions can cause similar symptoms, especially if the patient has recently increased their intake of lactose or other potentially irritating foods.

Celiac Disease: An autoimmune reaction to gluten that can cause diarrhea, abdominal pain, and fatigue. It's crucial to consider this diagnosis due to its potential for long-term complications if left untreated.
Giardiasis: An infection caused by the Giardia parasite, which can lead to severe diarrhea, abdominal pain, and fatigue. It's particularly important to consider in individuals who have recently traveled or have been exposed to contaminated water.
Colorectal Cancer: Although less likely in a 35-year-old, it's essential not to miss this diagnosis. Certain types of colorectal cancer can present with changes in bowel habits, including diarrhea, without the typical symptom of blood in the stool.

Whipple's Disease: A rare, systemic bacterial infection that can cause diarrhea, abdominal pain, and fatigue, among other symptoms. It's essential to consider in patients who do not respond to standard treatments for more common conditions.
Short Bowel Syndrome: A condition that can arise after a significant portion of the small intestine is removed or is not functioning. It leads to malabsorption and can cause severe diarrhea.
Tropical Sprue: A rare condition that affects the small intestine's ability to absorb nutrients, leading to diarrhea, abdominal pain, and fatigue. It's more common in individuals who have traveled to or live in tropical areas.