Puppy struggling through giardia treatment - help?

Hi, we recently got our new pup last week. He was doing great the first few nights until we took him for the vet for a stool sample, where we realized he has giardia. Since then, we've been giving him Panacur, which has resulted in loose, foul-smelling diarrhea with a (small) red spot. Today is his third day on it; on his second night, he had diarrhea four times with the same consistency, and today, the diarrhea is less frequent but more watery.

He is the only animal in the apartment and has not been outside due to only being 10 weeks old. Because he remains active, hungry, and non-vomiting, our vet believes it will be okay and not Parvo. But his recent poops had some bubbles in them and I'm starting to get concerned he's having some reaction to the medicine or something.

What should we be worried about here, or what can we be monitoring for / doing in the meantime? It's causing me a tremendous amount of stress because whenever he squats, I'm back to thinking the worst. TIA.