If I were you I really would see another vet. My sister's dog was a buffet of parasites as a puppy - bad stuff: worms, giardia, coccidia, and her local vet said he was fine and told her to give chicken and rice. She tried everything, probiotics, raw, etc. Then FINALLY, after many weeks of trusting that vet and thinking things would resolve themselves, went to a new vet and got the tests and meds she needed to kill the parasites.
I really hope you'll try a new vet. Some vets really are just not very good, while others, the ones we stay with and keep our pets well, are wonderful.
(a.k.a. Lucky's & Sparky's mom!)