Why arn't changes I am making in CSS appearing?
I'd turn off CSS aggregation temporarily to see if that makes any difference. The settings are in admin/config/development/performance

That way you can see which CSS files are being used directly. This sounds like it might be a configuration problem with the server itself and not something with Drupal.

Also, check the response headers for the CSS. That will give you more info about whether it's serving cached versions and if there's something like a reverse proxy serving old versions of the files.