Help! My pet rat is bleeding!?

I bought a pet rat a couple of days ago. She's been the sweetest thing, but today I noticed she was bleeding from her little rat . I don't know if I've been feeding her wrong or what. I feed her Reggie Rat food and I will cut a baby carrot everyday and give her the circles. I've also been feeding her apples and bananas but not a lot of them. Can some one please tell me what I need to do to make this stop?