Why is one side of your nose blocked?
Inside the nose there is a dividing wall, the septum, and on each side a set of swelling structures called the turbinates. They take turns narrowing and opening through the day. That rhythm is normal, and most people never notice it.
What is less usual is one side that never opens properly. A septum sitting off centre, a turbinate that stays enlarged, or the two together can hold that side closed. A spray can shrink swollen tissue for a while, but it cannot move a wall.
This is why the examination comes before any recommendation. Once the shape of the airway is visible on screen, the reason for the blockage is usually clear to both of us.