I get this awful condition from time to time, but fortunately usually with years in between bouts of it.
Have any of your doctors recommended Cawthorne Cooksey exercises? They involve slowly turning your head from side to side, then up and down which trains the brain to ignore the false balance symptoms it's receiving which cause the dizziness and nausea.
A physiotherapist came to my home to show me how to do them, then came back again after a few weeks.
If the balance problem goes on too long, it's worth considering being referred to a specialist at a balance clinic in a hospital. Not all hospitals have them, but the doctors there are expert in dealing with all manner of balance problems, and are far more knowledgeable than ENT consultants.
I believe they can even treat symptoms associated with Menieres disease, which is different to BPPV and more serious.