A dry cough lasting over 20 days and disrupting sleep can be exhausting, but it is a common issue that is usually manageable. For temporary nighttime relief, you can try an over-the-counter cough suppressant containing dextromethorphan, or a sedating antihistamine like diphenhydramine, which can quiet the cough reflex and help you sleep. Warm water with honey can also soothe your throat. However, because your cough has lasted nearly three weeks, it is important to consult a doctor. They can identify the exact underlying cause such as allergies, acid reflux, or post-nasal drip and prescribe targeted treatment to help you recover fully.