Lower right side of back is cramping while I run...

Question
Afternoon,
I'm training for my first 5k on the 23rd of this month. I been training for the past few months with very little issues. It's been a struggle running 3.1 miles, but conquered that. Now my issue is, I've run a handful of 5k's on the treadmill...recently have starting doing road running and that is when I cramp and only in my lower back, left side. It's strange, but has happened everytime I've done road running. I am running with the correct shoes ( I pronate ) so, I have a shoe that compliments my feet and got these from a runners specific store. The cramping typically happens about a mile to a mile and a half into the run. I slow down a bit and sometimes walk, but it is a real endurance zapper. Any advice would be greatly appreciated.

Answer
Trey,

Believe it or not, treadmills use different muscles and change your running form. You are likely used to treadmill running now, and when you run on the road, with different stress and form, your back hurts. Try running on the road more.

Ryan