How to stop my guinea pig from biting!!?

I've had my guinea pig for a week, and EVERYTIME I hold her she chews/bites on my fingers! At first she only nibbled but now she clamps down on my skin and pulls and it actually hurts so bad I don't really enjoy holding her. I love her though, and do it so I can bind with her. I hold her and support her, and wash my hands before, but she still bites. How cani get her to stop??