I need to lose 20 pounds?

I don't think this is a good plan. Really, you've got to be careful about how fast you drop weight. One pound a week is a great place to start, and certainly never shoot for more than two. It's dangerous. A pound of fat is equivalent to about 3500 calories, so if you are diligent to eat about 5-6 small meals a day that total up to about 1500, you'll keep your metabolism going, and lose weight faster. Ab exercises 20 minutes a day would be sort of pointless at this point, because you can't target the fat that you want to lose. If you wanted to see abs, you'd just need to do tons of cardio, like the swimming you were talking about. Some folks think that starving themselves is a good way to lose weight, but those people are the ones that don't succeed. I strongly suggest getting involved in some sort of program that has a nutrition plan, as well as an easy to follow exercise plan that will keep you interested (I use Beachbody's ChaLEAN Extreme). I think that in about 2-3 months, you'll be able to get all the weight off if you really focus, and it'll be so worth it!