Hypercalcemia has a variety of causes, with primary hyperparathyroidism and malignancies being the most frequently reported. We present the case of a patient presenting with chronic abdominal pain, constipation, and weight loss who was found to have hypercalcemia. The patient was initially diagnosed with colonic actinomycosis, but further investigations revealed an intra-abdominal diffuse large B-cell lymphoma (DLBCL). We suspect that the leading cause of hypercalcemia was the DLBCL, likely exacerbated by actinomycosis. Actinomycosis and DLBCL can have a similar presentation, so misdiagnosis or coexistence of both conditions should be suspected when a lack of response to one specific therapy is observed.