Is it normal that i get much more tired after i stretch or yawn?

yawning is done to activate body muscles and promote blood and nutrient circulation *including oxygen*. so yawning is body's way of saying that you need some physical activity!

I even get tired when animals yawn. Even if a cute little white mouse yawns on tv I think, "time for a nap." If my cat yawns and stretches then it's settled, we're taking that nap together right now.

That's the same for me too. I don't think yawning is meant to awaken you, but rather is a sign you need more rest, and I find that stretching at night helps me sleep better.