Have you backed up your phone to iCloud or a PC? If so, next time you sync it, it should restore all your music.
I've just been looking at the new iTunes, and once you connect your phone to the PC, open iTunes if it doesn't automatically start, up on the top right a selection appears for 'iPhone', click this, it should open the phone options, and a summary field will appear. This is where you can sort your backups and syncs. You can also click on the Music field, and it will show you what music is on your phone.
Updating iTunes and the iOS shouldn't wipe anything, unless you've somehow selected a full restore.