If you have no other health concerns, I would strongly recommend you start losing the weight now. I do not believe in willpower, which doesn’t last. I do believe in slow weight loss combined with regular exercise. See the overweight topic.
If you gained 30 pounds during pregnancy and haven’t lost it by the time you get pregnant again, then you may have even more weight to lose after the birth of your second baby.
Breastfeeding actually increases your metabolic rate to about 2300 calories per day (non-pregnant women need about 1800 calories per day). The amount of breast milk produced is dependent on your calorie and fluid intake. Some women lose weight, some don’t breastfeeding.