There is no really fast, way
to lose weight healthily. I agree with using the food tracker
to see how many calories you are eating each day, then start making small changes, like drinking water instead of soda (including diet soda), or snacking on raw veggies, rather than a candy bar, yogurt in place of ice cream, etc.
Exercise is essential to losing weight AND being healthy. There are exercises you can do that should not bother your asthma.