Thank you all so much for your kind words and your purrs.
We're very fortunate to have gotten a chest xray of him, he'd been treated about a month and a half ago for what we all thought was asthma. He responded really well to the steroids, so when he was having trouble breathing yesterday we thought it was the asthma. He stayed at the vet overnight, and I spoke to the vet this morning, and we decided to get him xrayed.
What the xray showed was a really, really large build up of fluid around the heart. His poor lungs were crushed by it, and his heart is pressing on his air pipe. This is what was causing the breathing problems, not asthma as we'd thought.
The doctor has removed a lot of the fluid, and his after xray looks much better, but they believe it is cardiomyopathy, which means that his heart is potentially failing.
We're going to take him to a specialist when he's able to travel, but the vet he's at is very, very good. He'll need to stay there till Monday at the earliest. He's getting the best possible care and he purred a little when we were giving him cuddles. I brought Thwack in to keep him company and one of his fleecy blankies. I also gave him his favorite Greenies, he sniffed them which was a positive sign.
Please keep purring for him. He is such a good boy, and so young.