Hi Bumblebee.
You're probably not going to see much weight loss from 500mg of Met. Is that a starter dose, or does your Dr plan on keeping you there? Also, did he suggest a diet plan for you?
Also, let me throw this in here - it is very, very important that you try and lose as much weight as possible before conceiving. You risk a lot of complications for you and your baby if you were to get pregnant at this weight. You've got time, just focus on getting healthy now so you can be a better and healthier Mommy.