Inflammatory Bowel Disease (IBD): Given the chronic nature of the lower left quadrant (LLQ) pain, decreased white blood cell count (leukopenia), and anemia, IBD (such as Crohn's disease or ulcerative colitis) is a strong consideration. These conditions can cause chronic inflammation leading to pain, decreased appetite, and subsequently, anemia and leukopenia due to chronic disease.

Diverticulitis: Although the CT and MRI are reported as normal, diverticulitis can cause LLQ pain and may not always show significant abnormalities on imaging, especially if the disease is mild or in an early stage. The anemia could be due to chronic blood loss from diverticula.
Irritable Bowel Syndrome (IBS): While IBS does not typically cause anemia or leukopenia, it can cause chronic abdominal pain. However, the presence of anemia and decreased WBC count makes this less likely but still a consideration if other diagnoses are ruled out.
Colonic Neoplasm: A tumor in the colon could cause LLQ pain, anemia due to occult blood loss, and potentially affect the WBC count, although this is less direct.

Lymphoma: Although less common, lymphoma can present with abdominal pain, anemia, and leukopenia due to bone marrow involvement. It's crucial to consider this diagnosis due to its significant implications for treatment and prognosis.
Chronic Infections (e.g., Tuberculosis): Chronic infections can cause abdominal pain, systemic symptoms like anemia, and alterations in WBC counts. Given the potential severity of these conditions, they should not be overlooked.
Sickle Cell Disease: If the patient has sickle cell disease, it could explain the anemia and potentially the pain episodes. However, the decreased WBC count would need further explanation.

Amyloidosis: A condition characterized by the deposition of amyloid proteins in various tissues, which can lead to systemic symptoms including abdominal pain, anemia, and potentially altered WBC counts due to bone marrow involvement.
Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Although rare, it could potentially explain some of the symptoms if there's a gastrointestinal involvement.
Whipple's Disease: A rare, systemic bacterial infection caused by Tropheryma whipplei, which can lead to malabsorption, weight loss, abdominal pain, and other systemic symptoms including anemia and changes in WBC counts.