Hi lzekkani,
Wow! 100 pounds in six months . . . very impressive! I am so happy to hear that you've made alli work so well for you - you must feel and look terrific.
Loose skin is a common concern with weight loss of your magnitude. Make sure you are combining cardio with weight training exercises. How fast weight is lost has a lot to do with how much the skin will tighten up. Rapid weight loss doesn't allow the skin time to slowly resume to normal, so losing 1-2 pounds per week is the healthy range, and what the alli plan is designed around. The younger you are, the more elasticity your skin retains, making it easier to return to normal. Although, depending on body composition, anyone trying to lose large amounts of weight can have some loose skin as a side effect. Therefore, slow and steady going forward is fine for you.
The key to getting tighter skin is to lose more body fat, (and build more muscle), creating a better muscle to fat ratio. Strength training is absolutely a critical component not only to keeping the weight off and burning more calories and fat even at rest, but also to helping minimize loose skin. If you are not already weight training, the alli recommended exercises on the Web site are a great start. Just make sure to challenge yourself with weight that, on your third set of any given exercise, the last few reps are difficult to complete and you have fatigued your muscles. Give each body part approx. 3 days in between training sessions.
You may still have some skin that sags, and that is unfortunately part of the reality. Some people opt to have it fixed surgically, but your best defense now is to keep going slow and steady and just know that what you are doing for yourself and your body is invaluable. You are giving yourself the gift of health - more important than anything else.
Good Luck,
Paul