Hi, this is my first post.
I was a runner 15 years ago and stopped running due to illness.
I'm 62 now and began the Couch to 5k yesterday.Whew!
I hope I can make it this time!
I had the same problem you mentioned about the muscle outside of your shin getting tight.
Mine would get so painfull and "swollen" I had to stop running within minutes.
I can't recall it's name but the muscles job is to lift your toes for your next step....
If you run uphill (not hill work, just slightly uphill) or an incline on the treadmill could aggrevate it.
Mine was healed with a massage called Active Release Technique (ART).
You can strengthen this muscle by putting your toes under a desk or something heavy and trying to lift it with your toes for one or two seconds at a time.
I hope this helps.