Having two babies close together. . .?

My son is now 7 months old. My husband and I want another child and we would like to have them kind of close together. But I gained 40 lbs with my son, and I am just now really starting to get into the dieting and strenuous excercise to try to lose the weight. And with the next one, I don't want to end up putting on another 40 lbs on top of the 40 I gained with my son. But I don't know if it will make a difference if I lose the weight now or not. If I go ahead and lose the weight, will it make a difference with how much I gain with the next pregancy? I don't want to do all this work to lose the weight now if it won't make a difference with my next pregnancy. But if I don't lose the weight, I don't want to have 80 lbs to lose after my next pregnancy. So, my question is, will it make a difference whether I lose the weight now? Or should I go ahead and have the next one, then try to lose the weight after that?