Fiction by Laura van den Berg.
At the beginning of this story, a plague has wiped out half of America's population. Unfortunately, the book does not improve from there, and the whole thing is very bleak. FYI: Don't stick around after the plague, folks. It stinks.
You may wonder why I would expect a dystopian novel like this to ever be anything but awful. (Remember The Water Knife? That was worse than this one.) I mean, if I know going in that it's about a disastrous future, why read it?
But the thing is, some stories about a terrible future are actually good. See The Stand by Stephen King for a much better after-the-plague story, or Life as We Knew It for young adults. And there's always Divergent!