How do I lose weight after having a baby?

During my pregnancy I had preeclampsia which helped me balloon up to 193 lbs. I have been stuck at 166 pounds for the past 3 weeks ( i had the baby 8 weeks ago) and I can't figure out why. I keep a calorie diary and remain fairly active. I never eat more than 1500 Calories/day and average around 1300. Why won't any of the weight come off? I want to get back to my 140 lb prepregnancy weight..