Hello and hope you are doing well.
The nasal block could be due to a sinus infection, a cold or a chronic allergy. It could also be due to a deviated nasal septum or nasal polyps. Sinus infection causes blockage of flow especially when a person lies down. The blockade is affected by the side to which the person turns also. You will need to consult your primary care physician for proper assessment. In the meantime practice good breathing exercises, humidify your room and do steam inhalations.
Hope this helped and do keep us posted.
One of the nostrils is always constricted, in a normally functioning nose, but it usually switches back and forth from left to right side. Maybe it's more noticeable because of your operation, but you might want to see an ENT again to make sure something else isn't going on.