My songs are erased heeellllppppp

Hello,
I downloaded music on my godmom's computer when i first got music and got more music and downloaded it on my home computer. ( last time my sister got games and downloaded on my home computer and i got the games so it backed up everything). So i pressed the erase and sync thinking it was already backed up and then this message popped up asking me if i wanted to transfer because itn said somethings were on my ipod but not my computer. Clicking transfer i left it over night because it always took a long time and came back this morning to find only the songs that i purchased on my ipod gone and the ones i just bought up here. What do i do?


TZ