A 15-day cough could be caused by an allergy, a viral infection, nasal discharge, asthma, acidity, or irritation from smoke and dust. It is crucial to see a doctor instead of continuing self-medication because many medications have not worked. In the interim, try steam inhalation, stay away from cold foods, dust, smoke, and strong perfumes, and drink warm water. Some patients may benefit from simple anti-allergy medications, but the best course of action depends on the true reason of the cough. If you get fever, wheezing, chest pain, breathing difficulties, blood in your sputum, or weight loss, get medical help as soon as possible.