Diva, actress, skinny legend, and local elusive chanteuse Mariah Carey is working on a memoir. A source has told “Page Six” Carey is “looking inward,” after disclosing her bipolar disorder diagnosis, and Carey’s reps confirmed she’s writing a book. “There were very few people in her circle who knew [she was bipolar]. It was a very personal decision for her. She’s been on and off medication since she was diagnosed,” the source told “Page Six.” “There was a small group of people who really cared for her, personally. They gradually left. There were a lot of issues. It was so layered. It was very, very bad.” Expect it to be a thin volume of Mimi’s musings.