My first questions would be, is he up to date on his vaccinations? Have stool samples been checked by a Vet and has he been wormed? Parasites, which are not unusual for puppies to have, can cause a number if systemic oribkems in the dog,mesp a pup.
Since you are taking him to work, any chance he may have gotten into something or any co-workers feeding him or sneaking him snacks? Not good.
You might try him on a bland diet of chicken (no skin) and rice for a couple of days. You could add a little canned pumpkin (not the pie filling) and feed a few smaller meals more often. This might be easier on the gut.
What food do you feed? Have you changed foods?
Of course, if his symptoms get worse, like the diarrhea or he starts vomiting, you need to get to the Vet.
A word of caution, and this may not be an issue with your dog, but this is one breed that can have adverse reactions to Ivermectin (Heartguard) if he had the MDR1 mutation. You might want to opt for another medication.
Good luck and please come back to update.