iTunes keeps deleting all my music from iPod 5

I have my preferences set to manually manage music, yet my music is regularly deleted. Most of my music is from CDs, and is stored on iTunes on my computer. Whenever I select music to add to my iPod, iTunes says it is preparing to update, then goes straight back to the default screen. I recently added music from my laptop, which was working fine until it also began doing this. Just today when I attempted to add music to my iPod, the preparing to update screen came up again, yet afterwards all music had been deleted from my iPod. This is not the first time that this has happened, and it is extremely frustrating. Can anyone help me?