Hi,

so sorry to hear about Fizz. what food does she eat? If it's mostly dry, then do try to get her onto mainly wet food, as the dry can certainly be a cause of cystitis and FLUTD. It's very rarely caused by infection, which is why antibiotics don't work. As has been said, stress can play a part but firstly I'd look at diet.
(see some of the other threads for discussion of appropriate foods for cats)

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