Difficulty breathing through the left nostril (cat)

Hallo,
I am looking for help for my one year old cat. He had a problem with breathing since he was little. During the examination, they found no obstructions (cyst, polyp,...) A swab from the nasal mucosa was positive for mold (aspergillus). He was given medication, but the condition is getting worse. He has a problem in his left nostril, through which he breathes with great effort. It gets worse after any physical and mental activity, lying down and in the evening. Then you can hear loud breathing rasping from his nose, similar to people suffering from enlarged adenoids. Half a year ago he got nux vomica for it and he inhales acetylcysteine, but it didn't help. In the evening he suffers so much that I can't sleep because I'm afraid he'll suffocate. But when he falls asleep, he often breathes cleanly and effortlessly, and no noisy breathing sounds are heard. Because of this, he is less and less active. He plays less and in shorter time intervals because he lacks the breath for it. About his character- He is very extroverted and friendly free soul. He gets bored of everything very quickly and still has a habit of insisting on what he wants. Thanks for every valuable tip.
[Edited by Suana on 2022-12-13 07:53:32]