Agree with blackanddom....stretch out your runs gradually. 3.1 miles is not actually very long at all once you've gotten used to running for distance. I started out from barely being able to run a half a mile through to being able to run up to 10 miles. I used the walk/run a lot in the beginning starting with a 2 on 2 off split eventually stretching it out to 6 on 1 off. This conserves your energy and mentally keeps you in the game to stretch out your runs longer. Eventually you won't even need to walk at short intervals. Give it a shot....I'm doing my first official 5K at the end of July just to finally do an actual race, but my regular runs are no less than 3 miles as it is now. My real target is on a half marathon by October, and then maybe we'll start talking full marathons by next year! Best of luck to you!