A constant cough in this setting definitely requires exclusion of:
(1) heart failure
, with other symptoms of shortness of breath
, unable to lie flat and swelling of the legs; an ECHO would be required;
(2) chest infection
, a Chest X Ray is definitely required;
(3) medication induced cough, the common one being ramipril or captopril or lisinopril
group of drugs.
You must see your Cardiologist to exclude the above 3 common causes, as only after seeing a doctor will he be able to exclude other rarer causes or causes more relevant in the current setting.
I hope this was useful.