Why can't I cure my diseases?

I have Skyrim for PlayStation 3, and in-game I have contracted 9 diseases.

Recently one of them has made my screen get considerably dark and my health drain. They don't appear in my active effects and no matter what I do, for example, drinking cure disease potions or go to a temple or shrine, they don't get cured and disappear.

I don't know what to do, and help would be greatly appreciated