Gastroenteritis: This is a common condition characterized by inflammation of the gastrointestinal tract, often due to viral or bacterial infections. The symptoms of abdominal cramping, diarrhea, and generalized abdominal pain are classic for gastroenteritis. The mild splenomegaly could be incidental or related to a viral infection.

Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can present with chronic or acute abdominal pain, diarrhea, and weight loss. The normal CBC and CMP do not rule out IBD, as these tests can be normal in early or mild disease.
Irritable Bowel Syndrome (IBS): Although IBS is a diagnosis of exclusion, it is common and could present with similar symptoms, especially if the patient has a history of abdominal pain and altered bowel habits without an identifiable cause.
Food Poisoning: Similar to gastroenteritis, food poisoning from bacterial toxins (e.g., from Staphylococcus aureus, Salmonella, or E. coli) can cause acute onset of abdominal cramping, diarrhea, and vomiting.

Appendicitis: Although the CT scan did not show appendicitis, it's crucial to consider this diagnosis due to its potential for severe complications if missed. Appendicitis can sometimes present with atypical symptoms or locations of pain.
Mesenteric Ischemia: This is a life-threatening condition that requires prompt diagnosis and treatment. It can present with abdominal pain out of proportion to physical examination findings, and diarrhea can be a symptom.
Intussusception: More common in children but can occur in adults, intussusception is a condition where a part of the intestine telescopes into another part, leading to bowel obstruction and potentially ischemia. It can cause severe abdominal pain, diarrhea, and sometimes a palpable mass.

Whipple's Disease: A rare, systemic bacterial infection (Tropheryma whipplei) that can cause malabsorption, weight loss, diarrhea, and abdominal pain. Diagnosis is often delayed due to its rarity and nonspecific symptoms.
Eosinophilic Gastroenteritis: A rare condition characterized by eosinophilic infiltration of the gastrointestinal tract, leading to abdominal pain, diarrhea, and sometimes intestinal obstruction.
Abdominal Lymphoma: Although rare, lymphoma involving the abdomen can cause a wide range of symptoms including abdominal pain, diarrhea, and splenomegaly.

Stool Studies: To check for bacterial, viral, or parasitic infections.
Endoscopy: To evaluate for IBD, lymphoma, or other mucosal abnormalities if symptoms persist.
Repeat Imaging: If symptoms worsen or do not improve, consider repeating the CT scan or performing other imaging studies like an MRI to rule out conditions like mesenteric ischemia or intussusception.
Blood Tests for Inflammatory Markers: Such as ESR or CRP to assess for ongoing inflammation.
Consider Empirical Treatment: For common conditions like gastroenteritis or IBS, while awaiting further diagnostic results.