If you have thick nasal mucus, cough, sore throat, and mucus but your chest is clear, it is usually due to an upper respiratory infection or sinus/allergy issue like Sinusitis or Common Cold; you can take steam inhalation 2?3 times daily, drink warm fluids, salt water gargles, and keep yourself hydrated, but if symptoms last more than a week, worsen, or you develop fever or breathing difficulty, consult a doctor for proper treatment.