If he's not losing weight and seems healthy otherwise, I wouldn't be too worried. He's maybe getting to an age where he doesn't need quite as much food and he's self-regulating. That could be a very good thing.
He's also getting toward that teething stage and that could also put him off his food a bit.
Things to watch for, though, would be lethargy, inability to poop, going off his food or water entirely, abnormal (more or less than usual amount) urination, shaking, unexplained panting, sitting hunched.... All those things could be a sign of something seriously wrong.
What are you feeding him, btw?
He sure is a doll!!!
Welcome to the board.