I took DS on a lot of walks when he was a baby.
And once I got him into a routine, it helped me get back on track as far as eating habits, exercise. But at first, I just didn't feel like doing anything 'cuz it seemed like I was forever feeding, changing, rocking, bathing -- he wasn't a good napper at first. And I was just overwhelmed with all the new responsibilities.
Just enjoy your little guy and don't worry about losing weight. You'll have plenty of time to do that in the future.