Blocked breathing through one nostril is often due to a deviated nasal septum, swelling from a cold or allergy, or a nasal blockage such as a polyp. Since salt water has not helped, try steam inhalation, keep your nose moist, avoid dust and smoke, and stay well hydrated to reduce swelling. You can also use a saline spray regularly and sleep with your head slightly elevated for better airflow. If the problem continues or worsens, consult a doctor to determine the exact cause and receive appropriate treatment.