My cat appears to have a serious hairball problem or poss asthma, please help i need adive as the vet is usles?

My cat is 18months old and since she was about 6months she has often had a hacking cough, like when they are trying to bring up a hairball. I have never seen her bring up one though. In the last four months she seems to do this more and more often often hourly. She seems to be out of breathe whilst doing it. Its is also triggered by me picking her up. My other cat doesnt have this problem. I spoke to my vet about it and she said it was a hairball and i should try using specialized cat food. I have been feeding her on science plan: hair ball treatment for about a month ( she was on royal canin urinary before as she get urine infections through crystals)and she also has been having katalax, these have not helped the vet doesnt seem concerned about this but i am, please help!!