I smoked for 15 years. When I quit I needed something else to do, so running is what I chose. You're gonna think I'm crazy when I say this but, people do not know how to run. They think they know, but they don't. I went through shin splints and foot and leg aches untold before I figured it out. Once I got it down I was good to go. The breathing Is the next thing. Once you hit that sweet spot and you get that runner's high you are unstoppable.
Make sure you have the right kind of shoes, breathe right and get your form down. Then think of me when you hit mile 3.