Until The Full Moon 1

Marlo has a problem. On the night of the full moon, this half-werewolf, half-vampire undergoes a mysterious and terrifying transformation: he turns into a girl! Desperate for a cure, his parents call on Doctor Vincent, a long time family friend. But Marlo wants to keep his condition secret from Vincent's son, the vampire playboy David. Unfortunately the secret gets out and a new problem arises: David is interested in Marlo's female form! If a remedy cannot be found. Their parents believe the next best solution is marriage - a marriage between Marlo and David!