I bought songs but they aren't on iTunes/iPod

My iPod asked me if I wanted to transfer my songs, and I didn't know what it was talking about, but I said transfer. So, now on iTunes it shows that I have 0 songs that I have bought even though I had paid for about 30 before this. After I synced it, all of my songs were deleted and now I don't have any of my gift card money or music. HELP!!!