Echoes, by Melinda Metz

Rae hears voices. In her head.

Rae, formerly known as Rachel, is the most popular girl in school, she's dating the all-star jock, has the best friends, and is wealthy. What more could a girl ask for?

Then, she starts hearing voices in her head that aren't her own thoughts and ends up in a mental institution for the summer.

Rae gets out by telling people what they want to hear - that the voices are gone.
But, as Rae goes back to school, and her regular life, she's still hearing the voices, all around her. Some are faded, some are loud, but one voice screams louder than all the others, and that's the voice that says "RAE MUST DIE".

Incredible story and amazing characters. I fell in love with every single one of them except one. I think that person is suspicious.... and I am SO hoping the next book is released soon so I can see if my suspicions prove correct.