[pugmomsandy]

The one on the left has poor body condition, where the one on the right needs to put on a lb or two.

http://i1326.photobucket.com/albums/u651/pugmomsandy/pictures%20for%20posting/IMG_28831024x768_zps49daa9d5.jpg

I would take measurements of your dog and keep a log of it and his weight over time.