I have been trying to find some kind of milk that Lindsey will drink. I have tried all kinds of flavored Lactaid milk and that does not seem to help by flavoring it. So I bought some vanilla soy milk and she seems to have developed a bad diaper rash but really no other symptoms. She drank it better than anything I have tried but if it is what is giving her the rash then I don't want to continue. How do you know for sure?