My 5 month old has been coughing for over a month now?

I took him to the doctor like 3 times and they all said the same thing that he is fine and he just has a cold. Considering the fact that he already has had 9 ear infections and only gets them when a cough and congested nose come with it...this cough will not go away and keeps getting worse. What should I do? I'm taking him to the doc today, but they are only going to tell me it will go away on it's own...it's been over a month now. Plus I think he has another ear infection...hes getting ear tube surgery on the 20th. Thank God!