Hi nerdsrock,
First off, congratulations on your weight loss. 100 pounds. Wow. You might be interested to know that for every pound you lose, it's 4 pounds less stress on your joints, so that's 400 pounds less that you're carrying around! I'm sure you must feel it. As for continuing to lose weight, a few thoughts.
1. You don't say your height and weight. Is it possible you've reached a healthy weight? One way to determine that is by BMI here
http://www.nhlbisupport.com/bmi/ A BMI of 28 if you are fit, which it sounds like you are, is associated with excellent health.
2. It's important to understand that plateaus occur with all weight loss. It's natural, and everyone experiences them. They pass, but sometimes it can take months, and again, it depends on what your weight is now.
3. You may need to reduce your calorie intake if you are still consuming what you used to (even if it's what you were consuming while you were losing). The reason is that you weigh less, and when you do, you need to cut back on calorie intake because you don't need as many calories when you weigh less. You can estimate your basal or resting metabolic rate (BMR) here:
http://www.webmd.com/diet/healthtool-metabolism-calculatorand then the Food and Fitness Planner to determine how many calories you need to lose more weight
http://www.webmd.com/diet/food-fitness-planner/summary4. As for exercise, you're experiencing what many people experience; that is, exercise doesn't help a lot with weight loss. It certainly helps because it burns calories, but you could run a marathon every day and not lose if you are consuming more calories than you burn. Of course, exercise is the single best predictor of keeping your weight off, and so it's important that you continue. And up to 35% of your weight lost can be from muscle, so it's important to keep up with resistance exercise to maintain your muscle. Muscle sets your metabolism, so you want as much of it as possible. You didn't mention what type of exercise you do, but it should include resistance exercise.
So, I suggest that you look at your BMI and healthy weight and see what's really necessary to lose; count your calories and calculate how many you need to consume to lose, and keep up with your exercise.
And most important, don't be hard on yourself. If indeed you need to lose more weight, then staying on plan will do it. But you have much cause for celebration. You've turned your life around with all of this weight loss and it's a remarkable accomplishment. Good for you.
Feel free to post back if you have more questions.
Rich