Music unplayable from iTunes, iPod shows no content under music

So, I'm not sure what happened here, but after adding a few songs to my iPod Touch, all of my music is FUBAR. Looking at iTunes, I can see all of my music, playlists, etc. listed just fine, but if I try to play anything, an exclamation mark appears to the left of it (and the song doesn't play, obviously). What's more, the bar showing how much space I have left shows that it's completely empty of music, it only shows that I have a few apps, some photos, and a couple of ebooks. On my iPod itself, my "Music" app says that I have no content.

I tried doing a manual restore on the summary page for my iPod, but it didn't change. What I don't understand (if someone could explain it, that'd be great) is that I have the option checked to automatically back up my iPod on this computer, but to the right it says that this iPod has never been backed up on this computer. Am I missing what the word "automatically" means here?

Is there some way to fix this short of redownloading everything and putting it back on? Thankfully I have a partial backup from when I last sent it in for repairs, but that was around a year ago, and I've added a fair bit of music to my iPod since then. And unfortunately, very little of the music on my iPod is actually in my iTunes library, because I hardly ever buy things from iTunes itself.