Hello! My 15 year-old sister has had a really bad cough for over a month (I'd even go as far as to say two months) that frequently produces mucus. Her doctor has prescribed her, on two occasions, with anti-biotics that she takes twice a day for about 10 days or so. But each time the cough never goes away; in fact, it improves while she's taking it then comes back with a vengeance once she done with her dosage. She's had x-rays and supposedly they come back negative, but why hasn't this cough gone away? I'm rather concerned and worry about her being sick for so long. Her doctor suggests a humidifier but I really wonder how much that can help. I think this may have began as a normal cold because she had other symptoms, stuffy nose, even a fever very briefly. Please help. Thanks!