switch from group exercise to jogging

So, I just celebrated my 50th pound lost since I began my lifestyle transformation, and I decided to celebrate by signing up for a half marathon. I spent the 6 months of my weight loss journey working out in the gym (on elliptical/stairmaster/treadmill) and participating in group exercise (bootcamp, Zumba, resistance training, body toning, cardio boxing). Now that I'm substantially lighter on my feet, I've decided to take up running/jogging. I was a cross country runner for 6 years (from 7th grade through senior year) and loved it. I literally hadn't run in 15 years until a month ago. I decided to run one day, with no particular mileage in mind, just to see how it felt. Well, it felt great, and I felt like Forrest Gump because, "I just kept on running". I ended up going 4 miles without stopping, which I was really pleased with. I think that all of my strength training and cardio workouts that my body was really up to the task, even though I didn't know it. I ended up running 3 times that week, each from 3-4 miles. I then decided that I would challenge myself to a half-marathon, with 10 weeks of training to prepare (knowing that I probably would not be able to run the whole thing, but at least put in a really good effort). I have been running 3-4 times a week for 3-4 miles at a time (at a 10 minute mile pace), and have enjoyed it quite a bit. The only thing I haven't enjoyed - I haven't lost a single pound since picking up running. I'm still awfully heavy to be putting that kind of pounding on my joints, and I was hoping that my weight loss would continue or even accelerate by adding this new component to my regime. I'm kind of shocked that nothing has changed. I haven't gained either, but certainly haven't lost. It could be that it's the holidays and my diet has been slightly less stringently monitored in the last few weeks, but certainly I haven't just blown it any one day. I'm eating anywhere from 1300-1700 calories per day. I'm hoping that perhaps my body is just making adjustments to a "new normal", and once it figures out that running is here to stay, it will start responding. I run on sand trails/grass when I can, or track surfaces, but do still end up doing a fair amount of pounding on pavement/asphalt. I really need to continue to lose. I'll just be patient.