Vampires as they appear in mythology do not exist. The undead creatures who cannot go out ion the sun or cross rushing water, who have no reflection--those are merely folklore.
There are vampires who have a sort of energy or prana leak, where they can't keep energy in the same way as normal people. Some ingest it through blood, which are called Sanguinarians, and some absorb it from people or living things, these are called Psi or Psychic vampires. A person who can feed either way is called a hybrid.
Awakening, the process in which you realise your a vampire, is very personal, and varies from person to person, but generally includes things like migraines, dizziness, obsessive thoughts about blood if you're a Sang, and accidentally draining those around you if you're a Psi. UV light generally causes problems, such as sun poisoning and extreme sunburns. (I can't go outside for more than 15 minutes without spf 45 or higher on, or I get sun blisters) and have issues with fluorescent lights as well. Like I said, it's different for everyone, but every vamp will tell you to go to a doctor and get normal explanations ruled out FIRST, without mentioning the word "vampire."