As a mom, you've got to fit exercise in between doing the toughest job in the world. Due to the nature of your "work," your 'me time' is very limited. Sleepless nights; taking care of yourself, a baby, and the rest of your family; being off a schedule. All are factors that disrupt your daily routine. Hence, you have to make the most of every minute, including your exercise time.
Short, brief, intense bursts of exercise will trim away the post-baby body fat, tighten post-baby muscles, and give you the energy to do everything you need to do on a daily basis. Not to mention, you're increased strength will allow for an easier time lifting and holding your child (think: multitasking will now be a breeze!).
If you can only get two days / week at the gym, do some outdoor fitness activities (weather permitting). Go for long, brisk walks while pushing the stroller. If possible, throw in some "interval training" by pushing the stroller uphill.
As for those two gym days, full body circuit training is the way to go! With one circuit, do upper body, lower body, and abs; and in the other, switch the order to lower body, upper body, abs. (ex: circuit round 1 - bicep curls, squats, crunches; circuit round 2 - lunges, pushups, hanging knee raises... keep switching the upper / lower body order for each round)
Cardio work should be done in an interval fashion. 40-45sec low intensity, 1:30-2mins high intensity, and repeat.
No workout (cardio or weights) should take you more than 45mins to 1 hour. I know you're tired, but keep the intensity up and you'll reap the rewards.
Food should be clean and meals should be small and frequent (5-6 meals/day).
For those moms without a gym membership --
If you're at home and the baby is taking a nap, fit in a quick circuit training session. Try some lunges, squats, pushups, situps, planks, side planks, and jump rope. You can even fit in your favorite exercise video. Investing in a set (or a few sets) of dumbbells will go a long way. Don't forget to get creative with your workouts. For example, use your furniture to your advantage. Grab a stable chair, or a couch, and do some dips for those triceps. Creativity and a routine are key - but don't be afraid to mix it up a bit. Get your baby involved. Do pushups as the baby lays on his/her mat. If you're out in the park, do burpees in between pushing your kid on the swings. You get the idea...
And most importantly...Remember, do not exercise until you've been cleared by your doctor!!!!
PS- Happy Mother's Day!