Why does my dog keep yawning?

While dogs may yawn when tired and may yawn when they wake up... most commonly, it's a different reason- it's another form of body language to communicate to other dogs, the human, or themselves. Often, it's a stress release and calming signal. Often, the dog is expressing it needs a break from whatever is going on, when they are feeling conflicted or stressed in an attempt to neutralize the situation or self soothe/calm themselves.

Your dog may yawn when presented with new situations, such as being approached abruptly or startled, having something or someone directly in his face, being picked up, when hugged, or when he’s unclear as to what is going on or what’s expected.