Giardia is nasty. My Golden Retriever had it. Picked it up who knows where. The meds worked pretty quickly though and she was feeling much better in a couple of days. She was a very large mature dog so she fared much better than a small pup would. Hope you get some answers soon.
). It gets bad reviews on the dog food analysis web site but its the only food she can eat without causing one of her flare ups. Here are a couple of links to it: