Why is my cat so anxious?

This is Cleo. She is 2.5 years of age. I have posted about her before actually. I worry about her because she gets so anxious that it harms her. She has had an outbreak of hives on her skin, especially her ears, for the last week or so, and she has been picky about when and what she wants to eat, if at all. We got a kitten in...