Thanks for all the replies, guys!
We visited the vet today for a routine checkup (11 pounds, and growing
), and turns out he picked up an intestinal parasite somewhere!
We got some anti-biotics that he will be taking twice a day over the next week, as well as special Eukanuba kibble that will help him get through it quickly.
He seems to like it well enough, seeing as he devoured it immediately
We'll keep him on the Eukanuba for now until the stomach issues go away.
Other than the diarrhea he's quite joyful - not house trained yet, but we're working on it, showering him with praise any time he goes in the potty zone in the apartment, or in the yard. Hopefully we'll be seeing results within a few weeks
I'll post updates as he gets better, thanks again to all of you!