Chronic nasal blockage with dry cough may be related to Allergic Rhinitis, sinus problems, a deviated nasal septum, or long-term irritation from dust and pollution. Nasal blockage can also cause post-nasal drip, which may lead to a dry cough. Helpful measures include steam inhalation, saline nasal rinses, good hydration, avoiding dust/smoke, and using a mask in polluted areas. Medicines such as antihistamines or nasal sprays may help, but they should ideally be used after medical evaluation. Since your symptoms have been present since childhood, it is best to consult an ENT specialist for proper examination and possible tests to identify the exact cause and long-term treatment plan.