You should know first off that a cough is a good thing, as it is one of your bodies self defense mechanisms to keep your lungs free from foreign particulates like bacterias and viruses.  So, while it can be uncomfortable and annoying, it is actually something that's good.

That said, why are you coughing?  Are you having an asthma exacerbation resulting in excessive sputum your body is trying to expectorate (spit up)?  If this is the cause, it can be treated with various asthma medications. 

Do you have a lung infection (like pneumonia)? If this is the cause perhaps your doctor might want to treat the infection too. 

Cough medicine may treat the cough, but it may not treat the underlying cause of the cough.  To find out the cause, and to treat it, you will need to contact your doctor.