So I've been walking around Riverwood as a Nord and most of the townsfolk are mentioning that I don't look healthy.

Can anyone think of why this might be? I'm just curious.

probs a disease check the magic effects tab or whatever it is shown

You have become infected. By a vampire.

You contracted vapirism

Go to the Spell list and click "active effects" and if you are being affected by a negative effect you will be seen as ill and NPC's will remind you of it.

@braves55

No its not just for vampirism in Skyrim.

A NPC told me earlier that I smell like a wet dog, lol.

Ah! Thanks everyone, it seems I have Rockjoint which makes me 25% less effective with melee weapons.