Tricia
You are so right about the vaccines -> Giardia link.
Parvo shot at 6wks & DHPP at 8wks (at breeder) then came home to me with Giardia at 10wks.
I didn't know any better and continued going back to the vet for Panacur & metronidazole along with more and more vaccines. Two years of this craziness, until I wised up. I'm floored by the money I spent.
With my second dog we avoided all that nonsense and went the nosode ($5) route until 9months. Now at almost 4yrs old, he has been exposed to parvo 3 times that I know of...And no issues.
My advice = don't even get on the Merry Go Round.