Yup, what Economics Crisis said.

If you want to lose weight, you need to burn off more calories than you're taking in. Simply exercising won't work.

In fact, it was proven that you can have an unhealthy diet, but so long as you're burning off more calories than you're taking in, you will still lose weight.

Try using an app like MyFitnessPal to track your calorie intake.

Can't upvote this enough.

Give this Couch-to-5k training schedule a try: http://www.coolrunning.com/engine/2/2_3/181.shtml