I am female, age 17 and weigh 140lbs. I used to be 120lbs before and now all I can do is think about losing the weight! I can't sleep right anymore, it's all I think about. If I run twice a day on a speed of 9 on the threadmill for 30 min each time, will I be able to lose those 20 pounds? PLEASE HELP!! :(

Stop fixating on the weight. It's a number on the scales that measures how much gravity is being exerted on your body. It doesn't say how fit or healthy you are, how hard you can hit a ball, or how you look in a pair of jeans.

By all means, clean up your diet (cut out junk food, sugar and white carbs, eat quality protein, health fat and lots of green vegetables) and get plenty of exercise, but do it so you'll feel good and look good in those jeans.

If you had no scales to weigh yourself, how important would this be to you?

Losing 20 ponds in a month is a very unhealthy and stupid thing to do.
Change your diet. Eat healthy, stay away from junk food and soda and have a regular exercise regimen. You'll begin to feel better in no time.
Also stay off the scale. Go by the way you feel and how your clothes fit.

The only way to lose 20 pounds in a month is to cut off a limb. Are you willing to cut off your leg just to weigh less?

Now, if you want to lose it HEALTHILY, then all you have to do is watch your diet and exercise. It'll probably take a few months. Most people only lose 1-3 pounds a week, which is healthy.

How tall are you? Height has a LOT to do with how the weight sits on your body. I weigh around 140, and people are generally surprised when they find out because I'm fairly tall. My sister is 5 inches shorter than me, so 140 pounds looks like more on her.

I'm 5'5 or 5'6

Then you're only an inch or two shorter than me. That's not heavy at all. I was thinking you were closer to 5'-5'2". 140 pounds on a 5'5"-5'6" frame isn't bad at all.

I know but I really am hoping to shed a few pounds in the next month or two, do you happen to know what I might be able to do?

Shedding a few pounds is all about diet, and looking good at your new weight is about exercise. Forget 20lb, you don't need to lose that much.

Seriously, you are at the age where you naturally will gain some weight to stay at your right weight. Look at your body as it is, not as you think it should be.

Watch your portions. Avoid fast food. Limit sweets intake. Avoid diet soda at all costs (the chemical that makes it 'diet' actually causes your body to store fat).

Walk to places that are nearby instead of driving. Ride a bike if you have one. Just get out and spend some time each day in moderate exercise.