Boy, I'm beginning to sound like a broken record... If you have a chronic cough for 25 years, I'm going to suggest something, you might laugh, but hear me out.
Go to a Holistic Dentist and find out if you have a mouth full of poisonous, mercury laden amalgam fillings in your teeth. You might have five, or twenty, or thirty. They leak mind altering, brain cell poisoning mercury 24 hours a day, 7 days a week - for decades and decades, and decades. It can be the source of your chronic symptoms, or this inhaled mercury can interfere with medicines you are taking which then can cause asthma, reflux, sinusitis, and many worse diseases over time, possibly cancer, and so-called neuro-muscular diseases. And if you smoke, that exacerbates the effects of these poisonous, mercury laden amalgam fillings. Every time you breath in, more mercury gets into your system.
Really, don't think it to death, get to a Holistic Dentist, fast.
Talk is cheap, but if that is what is wrong with you, you can become better, but the sooner, the better.