Why did my ipod delete all of my music when it was plugged into itunes and i tried to add an album to it

So i plugged my ipod into itunes like normal because i wanted to add a few new albums to it. Everything was fine, i dragged the albums to my ipod and i thought it was fine but then i checked my ipod just to be sure they were there and all i saw was the stupid u2 album that no one liked. My music is empty and i tried to see what happened and i cant figure it out. sadly i dont have my music anywhere else so im at a loss. What do i do??