to see what if you are a vampire check active effects and see if its listed.
you can cure the first three stages of vampirism via blessings from shrines or cure disease potions.
in the latter stages its harder to cure because you will be attacked, to reduce the stages you will need to feed on some hapless person or other and then use the shrine/potion.
a more drastic fix is to become a werewolf...
edit: oops forgot: if you been a vampire for more than 4 days (i think) you will need to lower your vampire level by feeding then go speak to an innkeeper (the feeding is so they arent hostile), this will direct you to a quest for the cure