Stray cat health concerns

Hey all,

New to this. Very new, but also very desperate, so I am willing to look foolish if the answers are obvious. I  recently took in stray I named Greg McMurphy because he was getting very sick outside and other cats were ganging up on him. When I got him to a vet, he tested positive for hookworms and FIV (though I am having him retested as I had a cat previously that showed up positive but then in all subsequent tests was negative!)

Anyhow, so he's been treated for the hookworms and an upper respiratory infection, but he has not stopped having very grainy, bulky, yellow diarrhea. He cannot seem to control it and will even just go standing up. He's eating and drinking normally, but he seems...sad. He's not his usual purring and lovey, energetic self.

Any ideas as to what can be causing this? I have been feeding him 9 Lives Plus Care and there have been no dietary changes etc. 

How "recently" have you taken him in? It can take a while for a cats digestive tract to settle while dealing with parasites. Is the cat kibble a new brand you're feeding him?

It's been at least two months. I know it sounds horrible, but I have been taking care of him so long on the outside, it all kind of blended in when he came inside. The brand isn't new. He's been eating  the 9 Lives since he has been outside and we were feeding him. I hope those little buggers ARE dead and gone (the parasites). I'm just worried it may be something of more concern or if I should be this concerned.