You can use a good probiotic joghurt for humans, Bird Bene Bac, Cani Bac, many companies have one your vet will know one. It is in discussion if anything of it comes to a dogs intestine because the pH of the stomach is so very low and kills most of the bacterias.
The intestins have a normal bacterial flora that is very important for their function and is a protection against other bacterias like Salmonella and pathogen Escherichia coli families (there a E.coli that should be in the intestines, not all are pathogen!) or Klebsiella or Candida (which is a fungus) and so on. When a dog has diarrhea a longer time the normal flora gets disturbed, especially in young dogs that are still building it up. You can help them with special diet over a longer time (there are commercial ones for intestinal problems that work quite good) but it takes some time till everything works really well, through this time your dog will be sensible to everything knew for the intestines, stress, bacterias and parasites.
I normally treat the Giardia twice, if diarrhea continues I send a sample to a veterinary lab for all parasites (inclusive Giardia again), mycological testing and bacterial testing. In Germany you can do this in one package and it is not that expensive. I also give every dog with longer problems a special intestinal diet until they have normal feces for about one or two weeks and then trye to change back in steps to normal food. The diet gives the intestines a rest and helps them to build up a normal flora again.
But this is how I treat it, your vet may have another opinion.
And again it takes time, don´t get to fixed on your dogs feces
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