Some of my songs aren't appearing on my ipod?

Hello,
everytime i sync my ipod some of my songs dont appear on my ipod there still on itunes well i dont really know how to epolain this heres an example of the songs that dont appear on my ipod.

!Here we go again by demi lovato

some of my songs that dont show on my ipod is because they have that !and then the name of the song in the begening i dont knoe what to do im so confused, then when i sync my ipod this little message pops up and it says "Some of the items in the iTunes library, including "Trash" were not copied to the ipod "Atzirys ipod" because they could not be found.

i dont know what to do please help.