Carlos' character is designed to be the silent type, the stoic guy, the emotional brick wall, etc. If you're saying he looks unhappy, that's literally why he looks like that, he's just meant to look like a big grumpy dude...most of Ben's inner dialogue when describing him is talking about his seemingly permanent, unchanging scowl he always has, but in the past, he looked like he was showing too much emotion when that isn't his character. Also, Ben is often found struggling with trying to figure out how Carlos feels, and it's usually only through his grunts or body language that Ben is even able to get a clue of that. And yeah I'm also sad that his overall physique changed, but some time is all it takes to get comfortable with it :)