I just returned to a town. Now no matter what town I enter everyone wants me dead. I know the sun is bothering me. Did I change?. What can I do. fix this I don't want to start over.

If youre not running Dawnguard its probably because youre a stage four vampire. If so it will be displayed in the active effects of your magic menu.
You will need to feed.
Travel to a place near a town, like the mine just outside riverwood.
Wait until its night, 2 or 3 am. should be fine, the villagers need to be sleeping.
Sneak into town and into a house. While sneaking click on a sleeping villager.
You will get the option to pickpocket or feed, choose feed and you will revert to stage 1 vampirism.
After 24 hours youll progress into stage two and so on, feeding will reset it to 1.
Speak to any innkeeper for the quest to cure vampirism, if you want to be cured.

If you're leve 4 vampire (without DG) they will attack you. What you need to do is feed on someone then talk to an inn keeper who will point you out to the guy in Morthal then you'll have to do his quest to cure yourself of the curse.

You don't have to feed on townsfolk either, just anyone who's sleeping.

EDIT Ninjaed