running

I really, really, really want to become a runner. I started the 9 week Couch Potato to 5K training program 9 weeks ago. I'm not running a 5K yet.
I did the Diva Dash with much disappointment and it has me really discouraged.
I joined a gym so I can run when it's hot or dark outside. I was loving the treadmill.
Lately, I'm struggling so bad. I can barely run 1 mile, I was running 2 easily just a few weeks ago.
So, what is going on? My right shin kills me when I run.....
People say that running is at least 90% mental. So, how do I get past this?
There's a 5K in a month that I really want to run with several of my friends.....
I also should prob say that I'm extremely frustrated by the fact that I've cut out 95% sugar daily and prob 98% of flour products and little to no weight loss.
So in my mind, why the hell am I still doing this?!