Tight calves

I think this might be just a streching issue but....

I am at the gym last night and I was going to do my 3 mile run on the treadmill. I strech for about 10-15 before hand, jump on and start increasing speed. I usually run a about an 11 minute mile for all 3 miles. Well I decided to push it for the first mile and cranked up the speed to an 8:57 mile and was able to run at that pace for the first mile. Once I hit that mile mark I slowed back down to a fast walk to catch my breath and all of a sudden my calves tightened up and got bad shin splints. I tried to pick up the pace and do my 11 minute mile and it was really pain full. it got to the point that even the walk was hurtting. I stopped after mile 2 as to not hurt myself.

Question?
1)Is it growing pains that I was feeling?
2)Should i have stopped and streched then started again?
3)Should I have just pushed thru the pain?
4)I went on a long bike and mnt. hike Saturday could this be a result?

Thanks for any and all advice
Steve