Suggest Treatment For Cold And Cough In A Child

My 15 month old daughter has had a cough for over a month now, worse as night but still contant throughout the day. It is a wet cough and I have seen many doctors about it, how say she will get over it, but its been over a month. I have tried a humidifier,keeping her window open, vicks rub...what do I do? She can t sleep properly because the couch keeps her up all night.