Right:
1) Go to the Doctor or Physio and get yourself checked out. See what they say.
2) Take a look at your diet, and cut out all the junk.
3) Get a personal trainer or somebody who knows what they are doing. Start doing some push ups, sit ups, pull ups, basic body weight exercises for a couple of weeks with light jogs. See how your doing.
4) If you're ok after stage 3, get your personal trainer to draw up a small workout for you. I presume you want to run again, so do some out door jogs, short distances at first and build up. Hit medium level weights, nothing that will injure you. Build up.
5) If you are feeling no pain, consult your physio/doc, get him to look you over. If he says he thinks that you could do more training, then up the intensity of your workouts and runs. Keep building up.
Good luck.