The trick was to nurse a lot for a full year to get back to my 130. But it took months, not 3 weeks! I am on baby #5 and never gained any lasting baby weight with baby #2 and up (after the baby was born and give it a few months, up to 9).
I run, nurse, eat healthy, and go to the gym 3 times a week. It's a lot of work but worth it!
I was shocked that the weight takes a few months to really fall off. But then it really goes fast if you do the above! I gained 19 lbs. with the first baby and a bit more for the others.
But still, before #1 I was 122 and 5'8" and that is never going to happen. My body is just different. I gained muscle though as I started going to the gym. I was 145 in college (same as 9 months pregnant with baby #1), and there I think I had way more muscle, even. I did a work out club that was insane 3 days a week. Good, but insane. :)