Ever since I finished Dawnguard I noticed something strange. I am literally inmortal, I cannot be damaged, my stamina doesn't drain, however I cannot use any type of magic that has an effect on me or shouts like Become Ethereal, meaning I cannot use Conjuration, Restoration and the majority of Alteration. I seriously need help with this!! Any thoughts?

lol That's awesome!
But I'm afraid you're on your own, bro.
Perhaps you should load a previous save?
Or maybe you could deactivate the Dawnguard DLC, and re-install it.
That might help, I'm not entirely sure.