A couple of days after he was born I was wearing a pair of jeans that had been too small for me before I got pregnant. Then I started eating badly because of boredom/not having enough time to cook a proper meal, and used breastfeeding as an excuse to eat lots of cakes because I needed the extra calories! And put the weight back on.
I haven't done any exercise since he was born, but then I didn't before I had him either. I'd say I'm about the same size I was, but my stomach isn't as tight.