What Could Cause Brown Spot In Left Breast?

I got a problem in my breast. My right side breast is in normal condition. But my left side one is looking different and also little bit bigger than the right one. The brown spot also is bigger than the right side one. Why it is like that? How to remove the brown spot? I am 20yrs old. I don't want a sexy structure. But I just want to be normal. Please help me....