What can you do for three sick pets who have already been to the vet but after four days the medicine hasn't worked and you can't afford to go back?
I would start by calling the clinic and asking if the pets should be better within four days - sometimes you don't start seeing improvement for a week or better depending upon the problem. If the vet states they should have been noticeably better, ask what can be done since you can't afford another visit. Your veterinarian may offer a payment plan or reduced costs on a return visit.
Another option is to check with your local humane society, shelter or rescue group - many of these groups have reduced cost veterinarians available or a Good Samiritan fund to help pay for situations like this.
Finally, if your pets are truly sick and suffering and you can't afford medication to treat them, you may need to take them to the vet for euthanasia - most veterinarians will offer very low cost or free euthanasia for pets that are suffering and owners cannot be treated.