Tammy2009 is right, you should use your rescue inhaler 10-15 minutes before you run.
I run, bike and swim, and I find that for
some reason, running seems to trigger my asthma more than biking and swimming. Back in the day, when I first started running, I was able to run about a third of a mile. I started with 3 mile runs. I'd run as far as I could, then I'd walk until I caught my breath, then I'd run again as far as I could, etc for the entire 3 miles.