Album's with no cover after syncing?

I recently decided to re-do my libary on iTunes. I deleted all of the songs, and in addition decided to wipe the music of my iPod. I then re-made my library which I made sure had all the music I wanted with album covers and then synced my iPod to this new library. I then had a problem with the artworks on my iPod. On all of the songs I had bought on their own the album covers swap around between these songs when I listen to them or select them which is pretty annoying, and also some of the albums I had previously will not show their respective covers, even though I have made sure my iTunes has them. I tried to delete all the music of my iPod again and then reinstall it but it has still left me with the same problem. Any ideas?