Forgotten (Forgotten Series, 1)

Each night at precisely 4:33 am, while sixteen-year-old London Lane is asleep, her memory of that day is erased. In the morning, all she can "remember" are events from her future. London is used to relying on reminder notes and a trusted friend to get through the day, but things get complicated when a new boy at school enters the picture. Luke Henry is not someone you'd easily forget, yet try as she might, London can't find him in her memories of things to come.
When London starts experiencing disturbing flashbacks, or flash-forwards, as the case may be, she realizes it's time to learn about the past she keeps forgetting-before it destroys her future.