Suggest Treatment For Persistent Cough

I am suffering from a severe cough. 3 years ago, when the cough first started, they found I have Thyroid cancer
and my thyroid was operated on. Now the cough is back. I am taking anti-acid medication but it does nor help
much. A friend of mine in Europe tells me she took a medication called LEVO and it solved her coughing problems. Do you know what pill is it ? What else can I do to stop the cough. I am 77 years old and I have emphysema.