I just rearranged my pictures from "Whatsapp" folder into different album using my computer but when I opened up the Photos section in my Lumia 920, the pictures doesn't show up and some folder is repeated twice. How do I fix this ? Thanks
First things first, do not delete pictures or folders that you think you have double in your phone.
Here is what i would do.
Copy the content of your rearranged folders to your pc and see what's happened in there.
If everything seems alright in your pc (check, check and double-check) throw away the folders in your phone, reboot the device and copy the folders back to your phone.