Studies have shown that journaling while trying to lose weight makes it more likely that you'll reach your goal and keep your weight off long-term.  Journaling provides an emotional outlet allowing you to get out frustrations or disappointments or set backs.  It can also be a way to motivate yourself.  Writing down positive mantras or tracking your successes can keep you on track. Purchase a journal, download a journaling app, or find an online journaling site to check in with on a regular basis.  You don't need to journal each day if you don't want to — even a few times a week counts. Jot down notes about your meals, progress, measurements and how you're feeling throughout your diet program. Having a support group is essential to weight loss — especially when you're trying to large amounts of weight.  It will take time to reach your goal of losing 100 pounds and it may be a long journey, and having a person or group of people to encourage and motivate you will be helpful.  Find friends or family members and tell them about your goal.  Ask them to help you stay accountable and encourage you until you reach your goal. Also try finding support groups in person or online.  Having people to talk to who are also struggling with weight or attempting to lose large amounts of weight will also help encourage and motivate you. The more weight you lose, the more motivated you will feel to keep going. But the only way to know whether you are making progress is to take regular measurements.  Weigh yourself once or twice a week. Be sure to do this at the same time each week. Mornings before you have eaten anything are best. Remember that clothes and shoes weigh something, too. For the most accurate results, weigh yourself naked or in just your underwear. Try to always be undressed or wearing the same thing when you weigh yourself for consistency. Take measurements. Use a tape measure to measure the circumference of your waist, thighs, arms, and neck.  As you lose weight and are working out regularly, you'll see your body shape changes as well.

Summary:
Keep a journal. Go to a support group. Track your progress.