They are testing his stool for Giardia. Why wouldn't they have tested that before? I mean Oliver has had almost everything a kitten could get to this point. Please don't let this be Giardia. In fact please don't let this be anything serious.
I've been following along but haven't commented much.
If he does have giardia, it's an easy fix. Panacur for 5 days is probably what they'll give you. Make sure that they do a float and a smear test though. Just one is not sufficient.
So I have a product that I use for kittens with bad poop and it also works for adults. And you can use it in addition to the daily probiotic that's linked above.
It's made by proag and it's called Benebac gel. I will link it for you, but it's basically a paste that you put in the cat's mouth or all of my fosters lick it off my finger.