What Does Constant Foul Smell In Nose Suggest?

I have a constant foul smell in my noise, have had it now since March of 2014. Met with my ENT. He has done a CT scan, an MRI and an EEG. Everything looks good and I still have the problem. My primary care doctor was very concerned and ran blood tests which came back normal. She suggested it could involve Alzheimers, MS or Parkinsons disease. I m getting really frustrated and discouraged. Why 1 year later do I still have this problem?