Around the US may be enough; for example (I'm not saying I think you might have this—just an example) in the SW US they have a fungal disease, Valley Fever—relatively unknown in the NE—I'd never heard of it until a couple years ago when I travelled out there, and neither had my doctor. There could be other examples of regional illnesses, fungal, viral, or other.

Another possibility is something environmental (also suggested by neurological symptoms). Any changes/remodeling at home or workplace, etc?

At this point, I'm spitballing to try to help you figure out any clues. Have you tried any of the symptom checkers? CDC? (Might take some searching—it's a large site.)

I wouldn't know about MS, but you're welcome to ask on the MS forum.

If you're still getting better—albeit slowly—that's a good sign; your body is fending it off. Hopefully in a short time this will all be moot.

Doc