My iPod wont put songs back on that I deleted.

I have deleted songs because I put album art on them and it wasn't showing up on my ipod or I wanted to add lyrics to them but when I go to put them back on my ipod and my itunes will act like it is putting them on there but they wont go on my ipod. I had the songs on there before so I don't understand why I can't put them back on. I've had this problem before and I used to be able to unhook my ipod and hook it back up and that would work. Then I had to shut down my computer and reboot it and that worked. I've even had to wait a day and it would work. Nothing is working now!! I just want to put my music back on my ipod!