Anyone who indulges in tasks such as Running, Lifting Weights, Yoga etc., without appropriate training, will experience the same difficulty as yourself.
Additionally, you state that you are overweight.
Therefore, in order to increase your running capability, you have to,
1) Reduce your overall body weight (assuming that you have a significant amount of extra Body Fat).
- Eliminate Sugary Drinks/Food (Colas and such)
- Lessen your Calories intake overall (not too much)
- Reduce your Carbohydrate Intake somewhat…
- Increase your Protein and Fat (all Fat except Trans Fat is Good) Intake.
- Keep a more Active Lifestyle (this, in addition to your Training for Running)
2) You will need to train for Running Longer Distances, by following an appropriate Training Program.
- Find a Good/Experienced Running Coach.
- A Good Running Coach will ensure improvement in your Running Technique and will provide you with a Training Program that is Appropriate for your Goals.
- Join a Group of like-minded Runners.
- You can get good guidance on Nutrition and about Required Gear (Good Running Shoes and such), from your Coach as well as from more Experienced Runners in your Group.
- Joining a Runners Group will also keep you motivated to attain your Goals.
That should do it.