OK, I went back and read all his symptoms. If he is eating, to get more liquid in him, try making him a mash with his probiotic water. Keeping him hydrated is VERY important. All of the medications in the world will not do him any good if his system is crashing because dehydration. Is he pooping at all? Do you have him separated from the other chickens so you can see what his poop looks like? I am no expert, I am simply telling you what I would do if this was my chicken.