I beg you PLEASE to discuss your weightloss aims with your Doctor first. Your goal weight (100lbs) would give you a BMI of 17.2. People with a BMI below 18.4 are considered underweight and at just as much risk of developing weight related health problems as are overweight people. Risks associated with being underweight include nutritional deficiency and osteoporosis.
Based on your height, to be within a normal BMI range you need to be between 108lbs (18.5 BMI - some doctors recommend a minimum of 20 BMI for non-asian women, which for you would be 116.5lb) and 145.5lb.
Please please talk with your doctor before going below this weight range so that he can make sure you are still healthy!