Odd question, but have you had any dental procedures done? I had my wisdom teeth out in 2015 and I was smelling all these bizarre odors for a couple years. Sinus issues too. I had a bad one in 2018 and I had such a bad smell in my nose I thought it was me and I was freaking me out so badly until my primary told me what was going on and put me on antibiotics and a nose spray. Then it went away.

Certain seizures can cause that too.