Hello, my boyfriends cousin has a female cat maybe 3 years old who was a stray before he took her in. Since he got her she has always had “allergy’s” according to her vet but she is always sneezing and more then half her sneezes she has green or yellow mucus that comes out with her sneezes and this is every day since he’s has her, it doesn’t get better or worse with anything he has tried. he has taken her to a vet but the vet says it’s just allergies and there isn’t much they can do. is there anything he should try to help out the cat ?