I would have given the same advice as the person before me...but being a single mom myself I find those things EXTREMELY hard to do! I know they would help me, as they do when I stick to them, but I find a hard time to do them.
I just wanted to comment on easy ways to add in excerise into your daily routine without adding too much time to your day...
Tummy tucks: Hold your abdominal muscles in for 10 seconds every time you stop at a red light and answer the phone.
Butt squeezes: While standing in line at the store, or sitting in a fast food line, squeeze your bottom in. It's something small that no one else will realize your really doing (unless their checking you out...whoo hoo!)
Have steps in your house? Take them twice each time you go up, go back down and go back up again on purpose. Crazy? It's a little extra exercise.
Sit ups first thing in the morning, when you get out of bed (or before) do 3 sets of 10 sit ups. They will help you get going in the morning.
Play time makes great exercise time, and when your child gets older they will realize that exercise is really fun! There are lots of examples online if you look them up. There are also baby and mommy excerise videos out there (or at least I'm thinking there are!) :)
Best wishes! Energy vibes to you!