Interesting, my main personal reason for reading post on this form is I suffer from chronic nasal congestion and have/do use prescription nasal spray, supplemented by saline spray and a nasal gel (forget the name, expensive stuff for over-the-counter), but none of this has caused me to detect smells, if anything I have a low sensitivity to smells. I am coming up on my annual physical and think I'll ask my primary care about seeing and ENT, perhaps I have an infection... worse I may have an allergy to everything.
They could be. An MRI would help to determine that.
IT could be that you suffer from sinus problems.
Infections can do hideous things to your sense of smell, taste, hearing, headaches, etc.
Just because you aren't congested or don't have nasty stuff pouring out of your nose, does not mean that your sinuses don't have some sort of issue.
As for just the smells alone...millions of people ( including myself ) suffer from phantom smells.
I smell wax crayons melting when I go outside.