how did i become a vampire and how do i get a cure for it ?
what did i miss?

Talk to a bartender and that should start the cure vampire quest, not sure if it needs to be a specific bartender or just anyone.

You can become infected with Vampirism from fighting vampires, it's quite easy to miss the message when in the middle of a tense fight. However over time you should see messages appearing on the screen about how you feel weak in the sun etc. and have a hunger for blood (I think), if you don't cure it (by accepting a blessing or drinking a cure disease potion) within three days you turn into a vampire, which means you have to do the slightly more arduous cure vampirism quest.

Go to Falion in Morthal. He helps you out easy

thanks i'll give it a try

every town i go into now...the townsfolk attack me....how do i get past this ?

Kill them all.
Joking aside, try to sneak in somewhere and find a sleeping person, then feed on them.

Feed on the Talos preacher and then go to Morthal. Seems like a popular hangout spot for vampires there.