Laying to Rest Childhood Mystery #4619-B

Perhaps you can help me with this. For months -- possibly years -- I've been trying to track down a young adult novel I read when I was ten or eleven. It's called Jem (no, not the National Book Award-winner by Frederick Pohl, though that's the only book the internet wants to tell me about), and these are the only details my spotty memory can yield:

The story starts at some point after the earth's population has been simultaneously afflicted with amnesia. The story is told, I believe, in the first person, by a narrator whose name I can't recall, but he describes how people try to deal with the confusion and aftermath of whatever has happened. A central character emerges in his narrative: a young man named Jem, who seems to have his shit together a little better than everyone else. As the narrator struggles with his own memories, which seem to be trying to resurface, Jem emerges as a possibly dangerous character who may have had something to do with the entire cataclysm.

I think. Like I said, I was only ten or eleven, and my precocious little brain didn't deal well with subtlety, ambiguity, and deliberately unresolved endings. My most vivid memory of reading this book was of perplexedly scrutinizing the last few pages before finally having to return the damn book to the library. And now I need to re-read it just so that I can finally lay to rest the burning question: WHAT THE FUCK IS THIS BOOK ABOUT?

For what it's worth, I've looked on Abebooks and Powell's. No luck. Any tips? Better yet, does anyone have a copy they can send me? In exchange, I'll trade you a book that actually makes sense.