My favourite YA book? Under Rose-Tainted Skies by Louise Gornall, for sure. A recent read for me, but that doesn't affect my love for it.
The instant connection I had with Norah meant that I whizzed through this and couldn't find a single fault with it. It's such an honest, open, real, and raw own voices account of mental health that it's a must read for everyone, whether they're suffering with their own problems or just want to learn a little more about life with agoraphobia and OCD.