anything under the sun

I'm really worried now for my baby. Her weight goes down and it's really obvious in her appearance. Just last week she started to loose her appetite though she still eats daily in regular basis but just yesterday she started not to eat. Even her milk she does not want to drink. She just taste every food that we offer her. I am asking her what's wrong and if she feels something, but she always reply "nothing". I don't know what to do anymore. I've changed her vitamins already but seems it's not working still, since this morning she still don't eat.