To me it sounds like you are trying to run too fast. Try taking your speed down to something slower, like 5.0 mph, and see how that goes.
Don't compare yourself to how fast anyone else can go--just find a pace that
you can sustain and stick with it. As your body becomes more efficient, and you become fitter, you will naturally find yourself able to run faster over time.
As for myself, I can run at 6.0 mph only for about a minute, too, since that pace is too fast for me to sustain right now. Instead, I cruise along at 4.2 mph for 40 minutes. That's up from the 3.5 mph I started at, and I am gradually getting faster as the weeks go by.
I know that in time I will get up there to the higher speeds, like 6.0 and so on. But for now, I'm content to chug along at the slower speeds and build up to it.
