Sorry you are having a rough time!! I'm sure this is scaring you. There is a chance that the ear issue is unrelated to your other symptoms. I have Eustachian tube dysfunction myself and will get a fullness in my ear, sometimes a ringing and the worst, dizziness on the level of vertigo (which often includes nausea). I had this chronically for a good long while until a visited an ENT that taught me how to do reverse ear pops (hold nose and blow, it pops your ears. Do it over and over). That straightened out my inner ear issue and now I only occasionally have an issue--- very rare, less than once a year.
As to the other, could you have a pinched nerve?
I'm glad you've addressed the vitamin D issue too as that has surprising effects on the body. Let us know if taking this helps and what the neurologist says. Come back and update!
I am just afraid thinking what if it's a tumor or anything serious.