The cat is spraying. I don't know what's wrong with her, the vet says …

The cat is spraying. I don't know what's wrong with her, the vet says everything is okay. She pees everywhere, even though she's been spayed. There's an awful smell in the house, you can barely breathe from the ammonia ?????? I can't take it anymore, we've lived with her for over 4 years, and now she's starting to pee all over the place, I bought sprays but they don't help.