You and I are in the exact same boat. I just had twins in March and now it's summer and I am completely uncomfortable.
However, I have found it helpful to build exercise into my day by taking the stairs, parking far away from the store, walking during my lunch, etc.
For me, I am having success counting every calorie that I put in my mouth...ie, gum, breath mint, etc. I have tried other diets ( atkins, slim fast, etc.) But I am not disciplined enough and fall off the diet after a couple of weeks.
Good luck! :)
What are you doing to try to clean up your act? The best thing to do to improve your eating habits is to get rid of the junk food and replace it with healthy foods, such as veggies and fruit that you can keep cut up and ready to eat at a moment's notice. Keep cartons of yogurt handy, instead of the pudding cups, etc. If you're that busy, you shouldn't have time to be sitting around, so should be getting plenty of exercise.
It's summer now, so you can put the baby in the stroller and go for a brisk walk. Even babies need fresh air and sunshine; if you live near a park, put the baby in the swing (most parks have swings with sides & straps that you can set the baby in) and push him very gently - exercise for your arms.
Turn your house work into exercise. "Dance" with vacuum or broom, do cheerleading while you're cooking dinner, get creative!!