I'm getting so tired !! of coughing!!! I've been taking the robitussin Dm that the doctor…

I'm getting so tired !! of coughing!!! I've been taking the robitussin Dm that the doctor recommended and it works sometimes but most the time no. I rub Vicks on my feet and chest. and I've still had a cough. for 3 weeks maybe 4 !! mucus is clear so its not a virus. but its sure as hell getting irritating.