Help find book I forgot about

Ok guys I can’t remember the title to this one book I read in elementary and it’s driving me nuts because I wanna read it again. I can’t remember a lot of the plot but basically
– high school girl, one of the main character name was Carson (I believe it was the main main character)
– suffers from amnesia I think because of a crash or something idk
– there’s a crime investigation going on I think someone died
– her father might’ve been a police officer i don’t remember I think someone who was close to her had that position
– throughout the book she finds notes but doesn’t know who puts them there
– I think at the end we find out it was her own doing, she was writing the notes
– she also had a bf or lover idk who
That’s all I remember and don’t think it was an elementary book, probably for high schoolers. Books were donated to my elementary that were inappropriate and my school gave them out to everyone without knowing how bad they were lol