What could be the real root cause behind my persistent dry cough?

Asthma/other lung dz: Peristent dry cough has many possible causes- including atypical pneumonia, chronic rhintis with post nasal drip is possible- also asthma or COPD which are chronic lung conditions. There are certain meds that can cause dry cough - so if you are on BP meds - check and see if you are on something that causes this. Go see your dr for eval- may do cxr and pft to eval.