Without a exam and review of your medical history I can reply in general terms and hopefully the following will help.
The nose is a complex organ that allows us to smell, to breath, to humidify and has a very obvious aesthetic component.
The main reasons for difficulty breathing is a deviation of the septum. The septum is a partition that separates the left nose from the right nose. If the septum is crooked it can impair airflow.
Another common cause of air way obstruction is overgrowth of the turbinates.
Simply stated the turbinates function as humidifiers for the air that comes in from the outside before it goes down into the lungs. When these turbinates increase in size they may block the airway.
Another cause obstruction that can occur are polyps. These are usually benign out growths with in the nose and can contribute obstruction.
Please make appointment/consultation with a Plastic Surgeon who is experienced in rhinoplasty procedures.