Getting back into shape after two years of no training

It will probably take you over half a year until you can break 18 again. Don't worry about the pace of your runs at first, but after a month or two, you can start pushing the pace on some runs, just going by feel, but not every day. Your pace will improve, but probably not at a noticeable rate. You'll be able to tell over time, but not day to day. Your back will probably feel better in a few weeks; you probably sit too much.

I wouldn't worry so much about weight training, but you need a killer core routine to add to the running.

Hamstring arch raises, calf strength work including calf bounces, squat holds, crab walks, glute activation stuff, ab and back work. Also flexibility (quads, hip flexors, glutes and groin are crucial).

Core twice a week, stretch every night.

Combine weight loss diet (no carbs at night) and running to start off with, then increase the running intensity as your diet gets back to normal and you start shedding weight.

These are both very helpful, thanks for the suggestions. The weight training is more for toning some of that fat so I aren't as scrawny as I used to be.

Since you're only running a half-hour or so a day, I'd use that extra time right now to hit the weights a bit more. Take more time between sets so you can go a little heavier or add an extra set or two for each exercise. Also, I'd start pushing the pace right now. When you hit the last half mile of your run, start picking up the pace and run the last quarter all out, 100%. Do this every time you run and I think you'll be very happy.

Yoga, a foam roller, and hot baths with Epsom salt should take care of the back.

Good luck!