My entire iTunes library is gone?

A couple days ago I noticed that the iTunes file on my compter had spontaeneously copied itself to the Pictures library on my computer. I had no idea why, but when I tried to move it back to the Music library I got a message saying that the destination folder is the same as the source folder. I wasn't quite sure what was going on, so I left it alone. Today, I went to open up iTunes on my computer and I immediately noticed that something was wrong. The Purchased tab was gone, replaced by an unfamiliar iTunes Match tab, and when I tried to go into the Music tab, it was completely empty. I went to see if my iTunes account had accidentally been logged out of, but it was untouched. I went into my Music library tab on my computer and clicked into the iTunes file. Everything seemed fine, until I realized that the iTunes media, the file with all my songs, was missing. I also checked the mysterious iTunes file in my Pictures library, and it was the same situation. I'm concerned because I have quite a few mp3 files I downloaded from 4shared, and I probably can't get them back since I didn't purchase them from iTunes. I do, however, have my entire music library on my iPhone, and I want to sync it with my computer and copy the songs on my phone back into iTunes. But, when I plugged my phone in and attempted a sync on iTunes, I got a warning saying that songs in my iTunes library would replace the songs on my iPhone. If I did that, it would virtually destroy all the songs I have on my phone. Is there any way that I can transfer the songs on my phone back into my iTunes library, without directly syncing with iTunes?

Yes, you can transfer the files from iPhone to iTunes, here is the video guide

and next time you may want to backup the files just in case losing them