Thanks for writing to H.C.M. for your query.
I have gone through your query regarding cough
for last three years. though you are getting temporary relief from tab telecast, this suggest involvement of allergy
since you are suffering from this for last three years , therefore few basic investigations are helpful to finalise your diagnosis. these are-
(a) C.T.scan of paranasal sinuses
(b) Culture and sensitivity of throat swab/ phlegm.
(c) Blood- CBC, ESR, blood sugar -( F. & P.P.)
After this much work one can reach to final diagnosis and that may be managed accordingly.