Blood in puppy stool

by Melissa
(Blenheim, SC)

I purchased my shih-tzu about 2 weeks ago. He is a gorgeous chocolate color (liver) and we have really fallen in love with him. We have been treating him at the advice of the breeder and the vet for Giardia because after we had him for a few days he started having blood in his stool.

The breeder said with her treatment of worming there shouldn't be any problems but wouldn't hurt to continue worming treatment. The blood has become less and less however on occasion he does have some blood. Now he has become constipated but we are still worming him at the same time.

Could the medicine the vet gave us for the Giardia be causing the constipation? He acts fine, eats and is pottying, but this morning he acted like he had to poop but couldn't. How long should I wait before I contact the vet? The little bit he did poop this morning there was no noticeable blood and after checking on him a little while ago, he was still doing fine, just hasn't pooped.

He is 12 weeks old. Any information anyone can share on this I would greatly appreciate.