Need some advice

My cat has been sick since august 1 and after a week i took her to the vet. I told the veterinarian that after she threw up a hairball she became sick with mucus,sneezing,lethargic and hadnt eaten since. He diagnosed her with a respiratory track infection in less than a minute. I got her tested for FIV and aids. Results were negative for both. He gave her a 10 day antibiotic shot and that was it.

Well it didnt work. Went back again and got another antibiotic. Still didnt work. She's had 4 different antibiotics and 2 refills and right now she's not looking so good. The only good results i've seen is that last week she's been able to eat and drink on her own. Before i was keeping her going with expensive af kitten formula milk. I've already spent hundreds. Im at a lost right now. If anybody has had a cat with something similar happening please message me with advice. I know little about being a cat owner since she's my first cat and she's only 2yrs old. I've already called the vet and they said they'll call me back. They never did so i called back nd the doctor left for the day...The lady said my cat was already on the strongest antibiotic. They'll call me back in the morning.

Also i sorry about not being active. Im already a adult and it's not like before that i had the energy to have my tumblr active or keep up with anime or manga. Things change as one gets older. 👵