First things first: have you got backups of those photos on another device or in the cloud?
If not make them right now! And those lost photos may probably be lost forever.
Next, install Dropbox on your phone and tweak its Settings to sync (when on WiFi!) every new photo in the DCIM folder on the phone. Then you will always have automatic backups in your Dropbox of every picture you take.
If you also have a tablet, or laptop or desktop PC, you can install Dropbox on that/those too so that you always have access to all your photos on all those devices.
Added benefit: you can always delete all your photos from your phone after syncing so that you can use that storage space again and again, because everything will be in your Dropbox cloud anyway.