Please Help! Got a new kitten and now these past few days have been a nightmare.?

Ok, I adopted this adorable 7 month kitten from the Humane Society last Monday and it's been a nightmare since, I noticed that the kitten had diarrhea the first day I brought him home and the odor was very strong, the next day he started to sneeze and had some drainage (clear) from his rt. eye, well I called my vet and made a appt. we had a snow storm so it got cx. till thursday, well in between my other 2 cats started to sneeze so I ended up bringing in all 3 cats, they took a stool sample from the new cat also well the vet started all cats on antibiotics,2 are on clavamox and the other is on Baytril and also eye oint terramycin 2 of them have to given that because she took a swab and it showed some bacterial cells in it, well on friday I got a call on the stool that they took on the new cat and it came back pos. for coccidial infection so she started all 3 on Albon liquid, well since I all these medications the 1 of the cats won't eat but is drinking some water the other got terrible diarrhea and vomiting, I was able to get in touch with the office on Saturday and was told to stop the clavamox on the cat who was having the diarrhea and vomiting but make sure to give the Albon, ok it's now Sunday the cat I stopped the clavamox started to vomit again, the other is the same and the only one who is doing better is the one that I got from the humane society, he still has diarrhea but has a appetite. so long story my 2 other cats that were not sick are sick now from the medication and the other one seems better but still has diarrhea. I will be calling the vet tomorrow but has anybody gone through something like this,this has cost me over 500.00 dollars already which I don't have to be paying for vets and this will set me back in paying my home bills, and also I called the humane society told them the story and they are going to have a supervisor call me tomorrow and they apologized to me and that unfortunately that this cat slipped through, oh it also had live fleas in it.He did say I could bring it back and I said yea after I spent all this money, but until I talk to the vet tomorrow I am stopping the meds on my other 2 cats because I am afraid they are going to get dehydrated and the cat that I got from the Humane Society I will continue the medications. he other 2 need a break and let there tummies rest.