My 2 month old baby has some kind of rash on her kneck and white stuff from it, what could it be?

Need to see doctor.: It's hard to diagnose based on your description. Possibilities include bacterial skin infection and yeast rash, so i'd advise seeing her doctor, as each cause is treated differently. I hope it clears up soon!

Yeast infection?: Make an appointment with her doctor, your baby may have a yeast infection on her neck. This is common but does require medication. It could also be a bacterial infection but not as likely. Keeping her neck area dry and clean helps prevent this from reoccuring once treated.