[TOMT] Please help me find a book from when I was younger!

There is a book I read when I was younger maybe between 2010 and 2015, I know that’s a wide range but I can’t remember exactly when it was. I will try to give all the details I can possibly think of. The book is a YA mystery about a high school track star who was murdered. The only person who would know who did it is her brother who was found at the scene of the murder but he has amnesia from that night. some of the suspects were the brother, ofc, the dad because he found the son at the scene and took him home, and the coach of the victim. If I remember correctly it was the coach that killed her because she was pregnant and was going to throw away her career. I believe the book is told from the sole perspective of the brother. Please help me I have tried anything and cannot find this book!