Music, (And Everything Else) Disappeared After Syncing iPhone 4S After New Upgrade

After the latest upgrade from iTunes, I noticed one of my songs wasn't where it was supposed to be in it's playlist, although it was still on my phone. After trying several times, I had no luck syncing it back into it's place. 2 days later, all of my non-iTunes music was gone from my iPhone. By some miracle, I was able to sync my playlists from iTunes, but not all of my music was on there, and those playlists are a mess. Has anyone been able to figure out how to get our music back to where it was and keep it from happening again?