If you were actually turned into a vampire the second time, the quest would HAVE to be available. This is always reversible, and you shouldl be able to tell soon if you are actually a vampire. You might be able to look in your active effects to see if there is some kind of effect from being turned into one. I recommend being a vampire actually, they are quite fun.
Source(s): Experience, beaten the game times
First, you change back automatically after a certain amount of time. The easiest way to do it is to just get to a safe area, then use the wait feature until you change back.
As for if you are one again, you can check your active effects section of you magic list. If you have the vampirism disease, it will show up in there. You usually have some time to cure it before turning.