I really think that you should accept your current limitations and work with those. Keep exercising, but at an appropriate rate rather than pushing yourself. I was in my taper for a mara when I first noticed my symptoms and I was determined not to let them stop me racing, but in the end, I had no choice.
It's not defeat, it's just pragmatism. Far better that you continue exercising at an appropriate level than you push yourself to a point that might have more serious consequences for your health. You are going to have the operation, so you will get better. The reason that you are struggling is because you are ill, not unfit.
I started running 5 years ago, since then, I've probably spent more time off my feet than on and have yet to complete an entire year of training. It's all due to circumstances beyond my control and ironically, none of which has had anything to do with running. However, I see running as something long-term, so when things are going well, I make the most of them, when the brown stuff hits the fan, I just accept it, adapt my training if I can, then look to pick up again whenever - even in this case, starting back pretty much at scratch.
I really think that it would be better for you physically and psychologically if you could keep exercising but in a way that doesn't leave you struggling, out of breath and feeling that it was a "horrible session".
But keep pushing on the operation, I had no end of prejudice being female - was even told "If you'd been a man, you'd have been admitted to hospital immediately."