Check if you have iTunes or iCloud backup of your iPhone first, if you have either of them, try to restore with previous backup.
iTunes and iCloud will automatically back up your iPhone even if have set it manually:
iCloud automatically backs up the most important data on your iPhone on a daily basis as long as your device is:
Connected to the Internet over Wi-Fi
Connected to a power source
Screen locked
iTunes can create backups of your iPhone automatically when you sync with iTunes (disabled if you have iCloud backup turned on).
But if you have no backup files on iTunes and iCloud. You'd better select some iPhone data recovery software to recover deleted photos directly. This method is very suitable for those often forget to backup data.
http://www.iphone-data-eraser.com/iphone-data-recovery.html
Remember to back up data frequently.