The fact that you get lots of infections and have nasty Post-
Nasal Drip points toward Point #1. If you have had no luck with antibiotics, or other forms of nasal irrigation, a Sinus Flush will be good option.
1. Some people, including myself, have had a smell that only they can smell. It could smell like dog-poop, old cheese, ammonia, a burning smell, etc. The smell comes on, often, as a result of a cold or sinus infection.