Hello, friend. You can backup your iPhone with iTunes, iCloud or a 3rd party backup tool. You don't need to lose your data. Even you didn't backup your data before iPhone factory reset, you can retrieve your lost data on iPhone with an iPhone data recovery. Tenorshare iPhone data recovery is such a tool that can recover deleted or erased files from iPhone witout any backup.
Learn more: http://www.iphone-recovery.net/how-to-backup-iphone.html (backup iPhone)
http://www.tenorshare.com/products/iphone-data-recovery-win.html (iPhone data recovery)