This might be a question to pose to your pediatrician. Maybe breastfeeding isn't the greatest time to begin a serious weight loss program, either, although I guess just eating healthier foods in general and staying away from junk food and carby stuff would probably help you get on the right path with it. Talk to your ObG about it, though.
N.B.: I'm not a fan of diet pills for anybody. Losing weight is best done by eating healthy foods so that you can learn the habits you need to keep the weight off once you've lost it. Diet pills won't do that.
Think about a low carb plan as well, especially since you have so much to lose. It can be rather discouraging to start a weight loss plan that promises 1-2# of weight loss a week. That puts you at about a year to lose your weight. Yikes. You could easily drop 70# much more quickly doing low carb. And quick weight loss motivates you to continue with the plan you've chosen.
Just something to think about.