I would call the vet and tell them you are bringing in a sample you want tested,
tell them his symptoms. You can drop it off, though, they can call you with the results. Chances are it will come up normal, but like I said, with these puppies being so small, little problems can get big in a very short time so it's better to be a little extra cautious. They will probably test for parasites?
Digging in the dirt? Yeah, who knows what the little bugger could have gotten into, these little guys are always into something!
Good luck, hope everything is okay!