I have to agree with Nat, (who doesnt agree with Nat) Metabolife has worked great for me. I took it before a cruise and lost 17 lbs without even stepping foot in the gym. The problem is that you have to change the way you put food into your mouth.
I took two caps before each meal and that was it. Most of the time I did not take any after lunch because you have a hard time falling asleep. Currently I am taking Metabolife only in the morning when your metabolism is at its peak to lose weight. The product does work but it is a precursor to speed.
With that said, hope you find it to work for you. how tall are you? 100 lbs is kinda skinny dont you think? Low carb eating and muscle tone may get you to 115-120 but it is a healthy weight. anyway, i am not a Dr. but college football for 5 years and have seen what happens when you go for the quick fix instead of long term goals.

good luck to you, join a forum or thread, the people here are great..