What Causes Nausea Along With Fullness In Ears And Vision Problems?

Hi, Over the past 18 months I ve had various episodes of nausea, imbalance, fullness in my ears, visual disturbances, at times after an episode i can walk with a gait. The biggest episode occurred last year where I was hospitalised for 5 days and was very off balance for almost 6 weeks. Neurologists have suggested it is a vestibular migraine. However, medication is not keeping episodes at bay. I believe this all began 18 months ago when I got off a plane after 4 hrs then jumped into a pool. I had instant pain in my left ear and felt like i was upside down and was thrashing about to get upright when I was already. Do you have any suggestions as to what the cause maybe? My neurologist is baffled and i think an ENT would be the way to go. Thanks Jac