Hi...regards form myself.....after reviewing your history..it seems you might be suffering from cough varient asthma...but as u said inhalers or preventers are not effective in your case, you must get your spirometry
test done...as that will confirm the diagnosis...ultimately corticosteroid inhalers are the best treatment for such problems...upon that you have not mentioned whether you are having any allegic symptoms like running nose , sneezing
, sore throat
...along with dry cough
...If yes, then definitely you are suffering from allergic disease..Get well soon...thalk u..