Thanks carman_liz for your input!
When the vet was here, she did look at his teeth and said that they weren’t too bad. Last time he got them floated was ~4 years back, and when the vet did them then, she said that he hardly needed them done. Prior to that, he’s only had them done once (He’s 17 this year). So he doesn’t get them done often (2 times in his life only), but it doesn’t sound like that was/is the issue. He’s been healthy for a few weeks now - eating well, good spirits, pooping ~ 10 times/day… but if he starts to show signs of colic again, then we will look into ulcers. We may also do his teeth just to be on the safe side.
We also just dewormed him again using a new dewormer in case the last one was no longer effective (we hadn’t been rotating through dewormers).