Where are my music gone?

Since the last update of the IOS and iTunes, most of my music are gone, why is that? How I retrieve them back? Is it through the iCloud? And I'm not sure the back up wouldn't work either.

Luckily, I have an old gene 2 iPod with all of the the music that I have. And I'm afraid that I might lose them on the iPod too. That I'll go direct to the technician at the store for that.