Hmm, maybe your media data got lost. You can force it to refresh by clearing media storage and then rebooting the phone. That is,
Settings > App Manager > All > Media Storage > Clear Data
Then, after data and cache are all zero's, back out to home screen, press and hold power button, and select Reboot. If this fails to bring your pics back into Gallery, then your card becomes the #1 suspect. If you have root access, then check your DCIM folder. If not, then I'd suggest removing the card and using a desktop computer to see what's actually on it.