Diffuse Large B-Cell Lymphoma (DLBCL) is the most common aggressive non-Hodgkin lymphoma, but primary Gastrointestinal (GI) involvement remains relatively rare. Diagnosing GI lymphoma is challenging due to its nonspecific symptoms, such as chronic abdominal pain, weight loss, and anemia, which can mimic benign gastrointestinal disorders. This case highlights a patient with persistent GI symptoms who was ultimately diagnosed with DLBCL, underscoring the importance of considering lymphoma in cases of unexplained GI complaints and treatment-resistant anemia. A 45-year-old female presented with eight months of persistent epigastric pain, bloating, and indigestion. Despite undergoing multiple endoscopic and colonoscopic evaluations, no active pathology was identified. Due to persistent symptoms and treatment-resistant anemia, a bone marrow biopsy was performed, which was reported as normocellular. Over the next two months, she experienced unintentional weight loss of 25 kg raising suspicion for an underlying malignancy. FDG-PET/CT was performed, revealing diffuse thickening of the bowel wall in the left abdomen and periumbilical region, increased metabolic activity in mesenteric lymph nodes, mild bone marrow uptake, and abnormal activity in the anal canal. Given the concern for a lymphoproliferative disorder, the patient underwent diagnostic laparoscopy followed by excisional mesenteric biopsy, which confirmed Diffuse Large B-Cell Lymphoma (DLBCL) of non-germinal center B-cell phenotype. This case emphasizes the importance of recognizing lymphoma as part of the differential diagnosis in chronic gastrointestinal complaints, particularly when associated with unexplained anemia and significant weight loss despite normal endoscopic findings. It also underscores the critical role of PET/CT in identifying occult lymphoma and the necessity of excisional biopsy for definitive diagnosis in cases where conventional diagnostic methods fail to reveal a cause. Early recognition and diagnosis of GI-DLBCL are crucial for timely treatment and improved patient outcomes.