Q: Music and Videos gone in iTunes. What do I do?

So I got a Macbook Pro for college this year. I had a Dell Latitude before and have had my itunes account for years. I havn't really messed with syncing my phone on my macbook because I havn't bought any new music lately. When I updated my phone to ios7, it put all my music videos and movies back on that I had removed for space. I went to sync my phone to my iTunes account today but it kept saying it would delete all my music, videos, ext. When I go to my iTunes library, it says that there is nothing there. I know i'm using the right iTunes account because I double checked on the Apple Support page. My iPod Nano, iPod Touch, iPod Touch 3rd gen, iPad, and iPhone 4 are all synced to my account that i've had for years.

I dont want to lose all my data that I've spent thousands of dollars on... What do I do to get it back so I can sync my phone and iPod again?