What's wrong with my kitten?

she probably has painful diarrhea, and is shying away from you because a cats belly is their most sensitive spot, and only if a cat is very comfortable with you will it show you it's belly, and it thinks you will want to touch it when you pick her up because you see there is something wrong with her, I would suggest taking it to the vet to get it some medication or just changing her food first, if it's not touching it that might mean it knows that is what is hurting it.