Have had symptom of imbalance for a year! Been to ent, neurologist had mri's! no diagnosis! Can you just have vertigo for no reason?

Perhaps these? You may have "paroxysmal vertigo", a migraine epiphonomenon, or you might have inner ear issues, such a meniere's, or perhaps, an endolymphatic fistula. Hopefully, anemias, thyroid problems, decreased blood vessel flow, and medication adverse effects have been eliminated. Never hurts to get an additional opinion at nearby medical school.
Difficult. Dizziness, lightheadedness and vertigo can be quite a challenge to work up, diagnose and treat. First, it is oftentimes difficult to sort out if its imbalance versus vertigo versus lightheadedness. If its vertigo, there are a couple of tests that are very helpful. First is an electronystagmogram. Another is posturography and an audiogram. If negative, it could be a heart or blood pressure.