Zerophilia (2005)

Luke, a young man insecure about his masculinity, must solve the mystery of his rare genetic condition, Zerophilia, that changes him from male to female anytime he's aroused--which noticeably complicates his love life. Journey with Luke into the wild world of Zerophilia to discover that you can't change your true nature, even if it can change you. A coming-of-age cult classic.