Same symptoms here, plus I smoke which exacerbates the dry, clogged sinus conditions. My right nostril plugs up within minutes of laying down horizontally and it can happen during the day if I forget to take deep breaths through my nose. I think in my case the cause is habitual and not due to a misshapen septum (for a long time, out in public, I slouched in my chair and took short, faint breaths so my big gut wouldn't stick out. I've lost 60lbs since then but the habit remains) and if it happens during the day, I can unclog it by sitting up straight and taking thick, deep breaths through my nose for a few minutes. The right one won't unclog until this breathing exercise dries out some of the excess mucous. If it gets particularly bad I like to take a hot shower and breathe through my nose, this fixes me up and leaves my respiratory tract feeling wide open and refreshed for hours.
As additional help for you, In combating this condition I studied about hydration and mucous membranes and how the body's water balance and the diffusion gradient are used to remove toxins from the blood, lungs, and mucosa. Basically, drinking a big glass of water very quickly can cause a rapid rehydration of the mucosa if they are dried out, as the water is absorbed and travels throughout the body, sweats out through the membranes, etc. This can loosen all the junk that can stick around up in the sinuses. Water naturally travels from where its concentration in a solution is high to where its concentration in a solution is lower. When you are dehydrated, the mucosa and other body parts which lose water constantly as a part of the natural water cycle, will dry out first and worst. In the case of drinking water you rehydrate them from the inside, in the case of taking a hot steamy shower, you rehydrate them from the exterior.
Hope some of this is useful to you.