You need to find a way to get him back to the vet. A cat not eating and drinking for a week? Perhaps talk to your vet and arrange payments. But he has to go back and be seen by the vet.

As I mentioned to the other poster - humanesociety.org has page on low cost or charitable organizations that help with pet medical needs - if at all humanly possible get the diagnosis because then you can make choices about what to do. As the old saying goes - if there's a will, there's a way.

Why did vet #1 prescribe antibiotics - based on what? Actually some of those can have some really nasty side effects themselves.

A diagnosis cannot be done online, although you may find people who like to speculate. Not eating/drinking is VERY serious, and there are so many possibilities that you don't want to waste time going back and forth speculating.

Once you have a diagnosis - at that point THEN you can find online communities to help you learn how to give care at home - things like administering fluids, running blood glucose curves, adjusting diet, etc. There are support groups for all kinds of things - kidney disease, cancer. ( A big shout out to Feline Diabetes Support Group - the best thing ever to happen on the internet!!!)