I haven't smelled it myself and don't know exactly what kind of odor it is. My guess, from everything I've heard spoken behind my back, is that it's some sort of fecal smell that gets stronger when I perspire. And people seem to react more strongly when they're behind me, so it's prolly, mostly centered around the anal area.
As for the mannerisms, I've experienced pretty much the same ones that you have. I won't go into too much detail, as I'm sure you've had similar experiences.
All considered, it seems way too much of a coincidence for this to be a psychological issue, thinking that people are talking about me when they're not. So, if it is true, I'm finding it very strange that medical professionals and my family are so adamant in denying the smell when they should be helping me to look for a cause. Things really don't make much sense either way I look at it.