@CakeLike: From what you've said, he's normal & healthy & nothing much you can do about his yawning, so you shouldn't worry. I'm just wondering when he's due for his next meal?
I have a hunch that maybe one of his teeth got loose & bent out of shape the last time he ate. If that's the case, it's likely to fall out with the next meal, so watch & see if he keeps yawning after the next time you feed him, okay? Something like a bent tooth would feel peculiar to him, & without hands, the only thing he can do is yawn, as snakes often do after they eat, just getting their mouth (teeth) realigned. As I said, this is just a guess on my part, but let us know if his yawning continues after the next time you feed him, okay? It might be that he'll stop yawning.