Hi nickie and welcome to the forums :ciao:
Try going to settings > apps, find the gallery app and select clear data and cache.
If that doesn't help try going to recovery.
Power off the phone, press and hold Volume UP and Home button. Now keep pressing these two buttons(VOL UP + HOME)and press power button for 2-3 seconds. Release the power button, but keep pressing Volume Up + Home Button until you see the recovery menu appear.
Use volume up and volume down to scroll up/down and home button to select an option. Select 'wipe cache partition'. When its done reboot and see if that helped.
If none of that helps the last option to try is a factory reset.