I had the same problem as well. It's because I had downloaded too many new versions of I Tunes and my I Pod was only syncing the 30 new songs I had added to I Tunes.
I clicked on my ipod and restored my Ipod. (It resets your ipod to the factory settings) *When doing so choose the option to automatically sync all of the music in your library * and- PRESTO! All of my music on my ITunes was synced. As long as they're in your Itunes Music Library they will be transferred.
It was as though I were starting with a brand new I Pod. Hope that helps. I was getting frustrated too. Don't get discouraged. :)