YA Mystery standalone book , read between 2008-2012, set in a college in USA. Girl attends self help meetings in school. Someone is poisoning students. Spoilers ahead.

[Lauren]

I read this book somewhere between 2008 and 2012. I borrowed it from my local library in the UK (now shut down and can’t check there). Protagonist is a girl who was just started college. I think the cover was prominently yellow and maybe had a yellow food in the title “ie, banana, custard etc”. On the first day of school the girl is sitting in the courtyard and oversees and argument between two students fighting over a laptop. The two girls were speaking an asian language, which the girl found odd, as if they were being secretive about something. (I think this ends up becoming an “ah-ha!” moment later on, important to the major plot point. Protagonist is made? to go to meetings/a club? in the school for the either social anxiety, PTSD or something similar. I can remember the older female group leader being “overly” excited and perhaps quite annoying and condescending. The protagonist often makes references to an ominous ticking clock at these meetings. She meets a boy at these meetings and they hit it off either as friends or romantically. Strange things start happening at the college and I believe people were either getting poisoned or found murdered. I think this is when the protagonist and boy team up to try and “solve” these crimes. I can’t remember much else after this apart from the very end when the “twist” is revealed. The boy and girl are either in an empty classroom, or a hospital, and the protagonist notices a math equation or science equation? written on a window or white board and puts two and two together and realises that the BOY is behind it! Just as she is realising this, the effects of the poison start to take effect on her - he got to her too. I THINK she survived and woke up in the hospital. I definitely don’t think this was part of a series.