Ucenter Dress prom garment suitable for plus size girl

anyone ever had a little pea sized lump in their armpit? Just noticed one under my right arm pit last night and it's begun to hurt (after poking and prodding it)...any suggestions? It's definitely not an ingrown hair or pimple, it's like under the skin, and rock solid. Ucenter Dress prom garment suitable for plus size girl :(