I’m sorry to hear that your music appears to be missing from your iPod. I’m not sure on the specific details of what occurred, but in most cases, that can happen if you initiate an iTunes Sync with an empty iTunes library which will replace everything on your iPod with what’s in iTunes. Our software simply copies the data and won’t remove any of it, and you definitely want to avoid syncing in iTunes until your library is rebuilt from your iPod.
As a last resort step, I would recommend still trying to use iExplorer to see if you can find any music files on your iPod by going into the file system and looking where the music files are stored. Just connect your iPod and then click on Media in the left panel of iExplorer (it has a house icon next to it), and go to the iPod_Control/Music folder, and see if your music is there and can be previewed in iExplorer. Any of your device’s music tracks will be in folders named F01, F02, etc. and each track will be named with four capital letters like “ATDF.m4a” . If you do find any of your missing music files there, you can simply drag/drop any of those files or folders to your computer, and when you add them to your iTunes library, the artist, album, track names, etc. will appear correctly. Those files are named that way due to Apple’s file naming system, but each of them still contain all of the important metadata for Artist, Album, etc. Once the files are on your computer, you can import them to iTunes by clicking on iTunes File menu > Add to Library and choose the folder.