Hundreds of paid for songs and downloaded songs gone with no trace. Has happened MULTIPLE TIMES! They were on my library a week ago and now are completely gone. Are on my shuffle but cannot sync back to library!!!

I have hundreds of songs that I have collected over the years, many purchased, others gotten from friend on their library. Hundreds have been deleted and are nowhere in sight. This is different that the exclamation mark next to the song (although I'm having that issue too!). These songs, I know, 100% exist because they were on my iPod shuffle that I updated about a week ago. Now that I have my new iPod, I wanted to put a bunch of songs from the library onto my iPod. There are some, but I felt as though I was missing a bunch of them.They are completely gone from my library and syncing my shuffle back to the library would delete them. This has happened multiple times before, and I end up having to re-buy some of the songs or re-downloading them from my friends library. Apple has cheated me out of money and convenience, and dare I say it, HAPPINESS!