I suffered from dizziness with nausea for 10 years and had every test and scan known, only to discover that it was the artificial sweetener Aspertame that was in everything I was ingesting. The diet Pepsi, light Jello, Etc. If you are eating/drinking anything with that crap in it, please stop immediately and see if you don't feel better. I began my improvement on my own and turned to a homeopathic alergist doctor to add to my therapy. Allergies can make you spin too.
Even if this doesn't apply to you, you have my support and understanding, It is unbelievably frustrating to deal with medical professionals. Wishing you a diagnosis and cure very soon. Please keep us informed.