Since MD's can't seem to find out what is causing your vertigo so badly I have provided 2 links to 2 types of chiropracters who just might be able to help you. Actually I have provided an extra link that has a video right on it's Home Page showing exactly pretty much what a NUCCA Chiro does to adjust the Atlas. Anything can cause the Atlas to not be completely level. And this bone is what our heads sit on. And when the Atlas is out of adjustment horrible vertigo can happen. There is a place on both of these websites where you can look for a doctor in your area. DO NOT be fooled. MOST chiro's do not have the slightest idea of how to adjust the Atlas. It takes a definite technique to do so. And any Chiro who says "sure I can adjust your Atlas" & cannot show you his certificate of having futhered their education by going on to school to become a NUCCA or an Atlas-Orthogonal Chiroprater then they absolutely CAN NOT adjust the Atlas. To find out if they have the credentials just ask them if they can show you them. They cannot cure RSD, but they sure can help with lots of other problems. They will not touch you without taking X-rays. And they defintely do not take hold of your head & twist it abruptly or by popping or snapping it. In fact after a few treatments by one of these types of chiro's you will NEVER go back to the other type again ever. I have been treated by both types. They both did for me what the other one did only they use a bit different techniques. But they both adjust the Atals, the top bone to our spines upon which our head sit.
They would be worth a try if you can find one near enough to you since the other doctors you have been seeing are not helping at all. Vertigo is horrible.

The frist link is to the NUCCA website:
http://www.nucca.com/default.asp
The 2nd one is to the website with the video of a NUCCA in action:
http://www.nucca.org/
This 3rd one is too the Atlas-Orthogonal
http://www.atlasorthogonality.com/introduction.htm