I'm a Nutritionist with a heavy focus on Parasitology.
The Giardia may well be water borne. If Giardia is the problem it must be eliminated. All the things the Vet can give you to 'take' won't stop the parasite unless the source is removed. Have you tested your well water? A water filter might be indicated but it MUST have a filter small enough [5 Microns I believe] to filter
Please check out the Hulda Clark Protocol which eradicates parasites electronically.
I believe it kills Giardia.
I have little faith in 99% of the Health Food products. There a couple of manufacturers with integrity but most just want to grind out a product to sell.
Probiotics will help but will NOT kill the parasites!
If you'd like further exchange, Q/A etc. I can be reached at