Well, I've been suffering from this for three monts now, and it is getting really annoying, I'll explain why.
One day i got up with a bit of lack of breath while i was breathing through my nose, but i didn't give it much importance as i thought it could be mucus or whatever, but it didn't go away, a month later I went to the doctor and she told me it was an inflammation of the "blood bags" in my nose, and was prescripted nasal steroids in spray. She reached that conclusion because i told her that while I sleep one of the holes of my nose, the one downside was very blocked and the other one remained clear, better than normal.
It's been two months of using that spray but it just eliminates the symptoms for a short time and then it gets stuffed again and it doesn't seem to improve.
Something I noticed is that when i stop breathing with my nose and I start breathing with the mouth and keep on doing this for around 5 minutes, my nose clears and I can breathe normally through it for a short time.