Try QuickPic--maybe it'll have more success in showing all of your pictures.
You could also use a file manager app like ES File Explorer to search your folders. Depending on whether you've set your camera to save to Internal Storage or External SD card (and assuming you're using the stock camera), you should be able to find your pics in /storage/sdcard0/DCIM/camera or /storage/sdcard1/DCIM/camera.