I have the exact same problem.
I tried restoring my iPod after updating both the iPod and iTunes. It seemed to have fixed it until I added more music to it.
I'm not sure if you're having an issue with the volume as well. For me, if I try to continue to play any music, the volume starts to adjust itself automatically and sometimes, even though I have the headphones in, it'll play the music outloud - and then will stop playing by itself.
It's frustrating and would love to know how to get this fixed.
All Apple told me to do was update it, but I did!