OMG! I got exactly like u. When I sleep on the side the lower gets blocked.
So my story is a bit more lengthy than yours.
For me the problem started after we moved to a hot humid tropical climate. After a few yrs I got worse and worse nasal congestion, at the end both sides got fully blocked. 24/7. ENT done a turbinectomy, but didn't help.
He gave me nasal sprays, didn't help. I tried immunotherapy, some drops under the tongue, didn't help.
ENT told me I was allergic to dust mites and the tropical climate wasn't ideal for my allergy, which was only partially true. It is true that I got dust mites allergies, but the real culprit, was just the humidity and probably the dust from the sugar cane fields. Took me 2 yrs to figure this out. I noticed when I left for a few weeks, went overseas, I got better.
So decided to move to a drier climate and my sinus problems improved heaps. However I still have that one side congestion at night, went to see an ENT about it, and he said it is just the way my nose is and surgery would be risky and might not help one bit. For me that one side congestion is ok, I'm ok to breath through only one nostril. During the day no problem at all.
Sometimes on bad rainy days I still get congestion, but never as bad as up there where we used to live, and once in a while using decongestants wouldn't hurt.
So my advice, if your ENT suggest turbinectomy think 2x before going under the knife. I didn;t have complications, but the surgery is not without risks. and for me it didn't help.
I don't know if you tired nasal rinse, saline sprays, there is no harm and who know, might be a bit of help.
Dust is a killer for allergy sufferers, so make sure you have no dusty carpets and stuff like that. When I vacuum I always wear a mask,
Anyway a CT scan would be a good idea, maybe you have deviated septum and an allergy test. It's skin prick test, and they will test the most common allergens.
After you have those tests, you might be able to find what's causing that congestion for you. They might always be able to, but without doing those first, you'll never know.
You can use saline rinse or spray meantime, wouldn't hurt.