BREAST CANCER????????

I am only 13. :( I know that breast cancer tumors are usually really small ... like a pea or a grape. But mine are big and they seem as if its just 1 big one in each breast. Both breasts seem to have the same structure and form of the lump. I am still going through puberty, so could it be the milk glands developing? Never had any history of breast cancer in my family. How long should they last and will they ever go away?