A lump that is located on the side of your neck could be caused by a number of things. Have you injured that area? If not, have you recently been ill? Injury can cause swelling that appears in the form of a lump. Also, illness can trigger your lymph glands to enlarge in response to the viral or bacterial infection. Autoimmune conditions, cancer, thyroid issues, cysts and even a bug bite can cause lumps. If it continues to grow or is painful I would suggest you contact your doctor immediately for an appointment for further evaluation.