My daughter has had a cough for 3 weeks now, and the medicine she was on didn't help. what could i give her?

No recommendation: After three weeks of coughing, and still the cough is present, i would recommend you see your pcp for a re-evaluation. Many things could be wrong if there is persistent cough. Asthma could be present, a foreign body could be present, a more serious infections could be present and others. See your pcp.

Depends: There any many causes for a prolonged cough and treatment needs to be directed. Causes can be infectious - viral or bacterial - the latter requiring antibiotics and the former time. Other causes include asthma, heartburn, nasal secretions, foreign body or other etiologies. When the cough lasts this long you should seek medical evaluation to help determine the cause and treatment.