Congratulations to you and Gus Gus on the progress. Some cats take a long time adjusting. I agree to confine Gus Gus to one room and put everything he needed in that room. Just act like he is doing fine and keep to a daily schedule of changing his water, food & litter. Talk to him and live him...
I hope your cat is better. Those shots sound terrible. Poor kitty! I am finger feeding my sick cat this canned food: Nutro Kitten Chicken Pate. It is nutritious and juicy. Order it from Amazon.
I am caring for my very sick Rainy (Persian) and have finally found a wet food she likes. I feed it to her on my fingers--Nutro Kitten Chicken Pate. I found it at Pets Mart. I hope your precious Buddy keeps improving. You are a good cat mother!