I hope they figure it out and find a way to get him better. I am SO sorry.
When I lost my old boy Fagan, just before the budgie boys came along, we all thought he just had a cough.. when it didn't get better with meds, it turned out a tumor had ruptured somewhere inside and his chest was slowly filling with blood. They drained all the fluid and told me he'd probably be good for about a week but that there wasn't much else to be done, but he was bad again within a day and we ended up at the ER for euthanasia.
It's so horrible and no one can make you feel better... but I hope at least you know you are doing EVERYTHING you can, and I hope it gives you some comfort that you've had time to try all the possible treatments. I really hope one of them works