I wake up with a stuffed nose every morning and is fine after 20 minutes or so for the rest of the day. Allergies?

Usual suspect. Allergy sounds like a prime suspect. It is really good that you are fine in so brief a time. In fact, it almost seems like risking side effects or building tolerances to any medications would be a mistake. Am i missing something? Is it difficult for you to bear those periods of time? You might try adequate hydration, non-allergic pillows & bed clothes, careful dust removal in bedroom, etc. Best!
Possibly. It could be or it could be the way you are sleeping. There is no need for concern but check the temperature of your room, this could also affect it. Hope this helped :].