Known as Chibi Vampire in the United States, this manga (Japanese graphic novel series) details the life of a family of vampires in Japan - with a twist. Most of the family are your usual, sunlight-fearing vampires, but main character Karin is different. Instead of drinking blood, she expels it. Once a month, the amount of blood in her body increases, and she has to bite somebody and inject them with her blood, or it will come out in a massive nosebleed. She's also immune to sunlight and garlic, and attends a human high school. With the help of her little sister Anju, Karin manages to keep her blood problem under control. Until a new student starts at her school, and Karin discovers that just being near him makes her blood increase.
This is a whacky romantic comedy that's definitely worth a read. The manga is complete in 14 volumes, along with a few side novels, which are all available in English from Tokyopop. In addition, there's a 24 episode anime series, also available in English.