What Causes Brown Patch Under The Left Breast And Light Bleeding?

Hello doctor, I'm 12 years old 5.9, and 220lbs. I went to sleep perfectly fine, but when I awoke, I found a brown patch under my left breast. It was first bleeding, clear liquid came out. On the third day, it dried, but it started to flake off. Now, it still has the brown discoloration, looks kind of cracked, and doesn't flake. Any idea of what it could be? My health history isn't that bad, just high colestorol (I lowered it, but still is concidered high)