I tried running a mile a week after giving birth...3 days later I was in the hospital for postpartum hemmorrhage, and being chastised by my OB, who had made me promise to stay off my feet for 3 weeks, minimum. I listened the second time and started runs with my little one in the baby jogger when she was about 3 months old. Like an above poster said, these runs felt so shitty I could cry...I also have a new appreciation for people trying to get in shape from nothing. I kept at it, though, and the week my daughter turned a year old, I PRed in my conference meet.
My advice is to take your time, and cut yourself some slack...you'll get there.