Hi, In January I Found A Small Bump On My

Hi, in January I found a small bump on my back and every time I touched it, it hurt a lot. My mother suggested that I leave it alone. Today, it was starting to irritate me. So, I squeezed and whitish gook came out. Additional Information: In January it was very small, the size of a small candy, like an M&M or something. Now it is feels like it's the size of a dime or quarter. Help?!