It's important to be careful about losing weight during the first weeks postpartum because your body is still trying to recover.
Starting about 3 weeks after my son was born (he's 8 months now) my husband and I would take him on short walks around the neighborhood right after a feeding. He got a great nap and we got some exercise. I wait until he was 8 weeks or so before starting an exercise video every other morning. By then his sleep schedule was more solid and if I went to bed when he did, I could wake up with enough time to work out and shower before he got hungry. I gradually brought up the intensity level and went from 20 mins to 30 while adding toning.
The most important things to keep in mind those first weeks are to rest, eat right, and drink plenty of water. I kept the house stocked up with cheese, crackers, and plenty of fruits and vegetables. I would recommend asking your doctor about increasing activity at the 6 week check up .