I was in exactly the same position as you a few years ago, savi.
Developed asthma for the first time in my life in my late 40s (quite a common time for the onset of it). I seem to be symptom free in the summer but as soon as cold weather comes I am affected. In fact during a couple of recent autumns I was struggling to breathe and had pneumonia-like symptoms that low-dose inhalers didn't seem to be touching. I was referred to chest clinic which I attended for a year and they gradually got the asthma stabilised. The type and dosage of the steroid inhaler has to be experimented with. (I think I was the only patient who ran 6 miles to the clinic and back!)
I start my current steroid inhaler about October time and use the reliever only when necessary, but always carry it with me in long races. A good tip I have picked up is to take 2 puffs of the reliever about 15 minutes before starting running and that sees me to the end of most events. You shouldn't need to use it every 20 minutes. I'm sure you'll find you'll be able to get your symptoms under control eventually once you start using preventers.
In the winter I've had to learn I can't race. In training runs I prevent myself breathing in too much cold air by wearing a buff over my mouth and when very cold over nose and mouth.
It's hard to know whether having asthma has slowed my performance since I am at an age where performances are likely to start slowing anyway, but I suspect it has a little. But I still do about 10 marathons or ultras a year and it hasn't stopped my enjoyment of running in the slightest.
Good luck.