I went home yesterday and reformatted my SD Card and transferred all of my music back onto it. Strangely enough, when my SD card was empty, Mixzing and the standard Android music player both said all of my music was on the phone, but I couldn't find it anywhere.
So I went through Mixzing and manually deleted all of my music and loaded everything back onto my SD Card. Music seems to work just fine now. Thanks for putting me on the right track