A cough that continues for around 20 days may happen due to a viral infection that has not completely settled, an allergy, sinus-related throat irritation, dust exposure, acidity, or a mild chest infection. Since your cough is more troublesome in the morning and evening, allergy, mucus dripping from the nose into the throat, or irritation from weather changes may be possible reasons. Drink plenty of warm water and other warm fluids, avoid cold drinks, smoking, dust, and strong smells, and take steam inhalation 2-3 times a day to reduce throat irritation and loosen mucus. Warm water with honey and ginger may also help soothe the throat if you are not diabetic. Try to rest well and avoid self-medicating with antibiotics or multiple cough syrups without medical advice, because the treatment depends on the exact cause. If you develop fever, breathing difficulty, wheezing, chest pain, blood in cough, weight loss, or if the cough lasts for more than 3-4 weeks, you should consult a doctor for proper evaluation. The doctor may examine your throat and chest and advise tests if needed to rule out allergy, asthma, sinus infection, acid reflux, or lung infection.