Why Whatsapp images and videos are not showing in my gallery?

I have bought Moto G 2^nd generation. I have Whatsapp installed in my mobile and it working very well. As you all know all Whatsapp images and videos will get displayed in gallery.

I decided to hide these images and videos. I have searched over net and found some useful links. Based on that, I have placed a .nomedia folder under whatsapp/media folder. After this, when I checked gallery, all images and videos from Whatsapp are gone. Eureka... Then I reverted the changes that I have made. That is I deleted the .nomedia file from media directory. But unfortunately, I couldn't find my Whatsapp images and videos in gallery.

So I cleared cache of Whatsapp via settings. Then I restarted my device. Still I didn't find my Whatsapp data in gallery. Now after getting some new images and videos through Whatsapp, I checked again. Now I can see those videos and images. But still the old images and videos are "hiding away" from gallery. Why?

I have checked Whatsapp folder. I can still see old images and videos in whatsapp/media folder and the new videos and images are added to the corresponding folders along with other images and folders.

How can I show all of my images and videos in gallery?