We really should have a sticky for how to cure vampirism...
Find a sleeping person and feed on them. Then people will stop attacking you temporarily. You have to do this every couple of days while you are still a vampire to keep them from attacking you. To cure it for good, go talk to an innkeeper (of course you have to feed first), and they will send you to the guy who can cure you. His name is Falion, and he's in Morthal, so you can just go to Morthal and talk to the innkeeper there, to save a step or two.
Edit: You don't know how you got this disease? You have a 10% chance to get it when a vampire casts the Vampiric Drain spell on you (looks like a red stream going from you to them). If you catch it, you should get a message at the top of your screen that you contracted Sanguinaire Vampiris (you can always see if you have any disease by looking at "Active Effects" in the magic menu--diseases show up in red). You have 3 days after that, that it can be cured by using a Potion of Cure Disease, or by using a Shrine in any temple. After that you become a full vampire and must do the quest to be cured.