Bad smell from nose that only I feel.

Bad smell in my nose only I can feel, only when I exhale, warm type of feeling in chest but no pain just uncomforting, history of headaches, weather changes is factor, one sided headaches and behind the eyes at times. Currently seeing an ENT, he gave me anti biotic to take for ten days and allergy spray, a little improvement but smell came back 8 days into the 10 day antibiotic cycle. Found out that drinking coffee brings out the smell more, and its sort of a dusty Smokey, stuffy warm odor but the smell is almost like a feeling at the same time. My ent is moving forward with a CT scan of my sinuses, and said my brief exams, looking into my nose with a scope and such are looking good. I did blood work and urine test on stds and other diseases just to be sure and everything came back negative. He said chances of a brain tumor are extremely slim based on the data he gets from my follow ups and exams. I just want to know what could this be? how far will I need to go to get an answer?