NPCs I walk past keep saying I look sickly, or I look sick. Is this just b/c the Nords aren't used to seeing Dunmer folk? ( my character is a dark elf), or is this because I might actually have a disease, and how do I find out if I do??

Go to "Active Effects" (Or something like this) in the Magic Menu.

It's because you have a disease. Go to any altar to get it cured.

I'm a Breton and they say the same thing to me. Do like the other said and this will cure you. You can also sleep.

Traps (mainly in dungeons) have a 25% of giving you a disease if you spring one.
The other 2 main diseases turn you into a werewolf and a vampire - you will certainly know if you contract one of these and the shrine method does not work on these.

As above, tab into menu, magic, active effects, it'll show in red any disease you have here.

Go to any shrine and activate it to be cured.

Thank you all for your help. I had "Rock joint" apparently =D