i have to constantly restore my ipod 120 gb and it won't allow me to sync (it does but they get deleted when connected again or ejected)

Ive been having this issue for a while now but I'm reaching a boiling point. I've had my classic 120 gb ipod for a couple of years now and just recently started having issues syncing music and i have to constantly restore my ipod because itunes forces me too. please help resolve this issue please.