Now a couple little tips - you can lie on your back and not do much motion right that's one way of having sex. Histamines is a great idea. You can do it in a cold room which is a turn off for the guys sometimes but it will keep you cool. And that's probably the most important thing. The less you sweat the less you'll shrivel up a little bit but you can still get an erection.
It's probably not gonna get better until you stop doing things that break sweats. Having sex is so important to your well being as a couple and to your over all health that you got to fight your way through it and you can. The only thing that makes me all worried about is when you say you get short of breath. So you ought to have one of those epipens near you just in case. Just keep it around because if you getting short of breath one day you really, really doing it and you're hanging from the rafters. You might actually need that. God Bless you.