I would suggest that due to the layoff your muscles tighted up somewhat. That is putting a strain on the connective tissue joining the calf muscle to the bone. I would try stretching more before/after running. Decrease mileage from say 4miles to 2miles to start. If you notice improvement then use the shorter run time to raise your overall speed. Then begin increasing milage on every other run. I think possibly the rise in weight coupled with the layoff is causing the primary issue. If you continue to run then there is not chance for the tissue to recover. You don't want to quit again but you need to get the weight down while you allow your body to heal.

I would say though that most weight gain issues reflect with pain in the knees and not shins. I'd also revisit what type of shoes you are using and whether they are right for your foot, ie arch support and width. etc. Good luck, because if you don't have someone punishing your body you may as well do it yourself. :-)