It's time to ask your husband for help.
He can keep an eye on a child for half an hour a couple of times a week so that you can exercise.
You don't have to hand him the kid as you walk out the door
but give him a little relax time from work, and then take time for yourself, woman!
Alternately, start teaching the kid to sleep earlier while you're still awake. Adults get to be awake longer than children do. I'm sure he'll think life's not fair for a while, but he'll eventually fall asleep and you'll have time to yourself to exercise, even if it's just for a little while at night.
You don't have to feel guilty about wanting 30 minutes to exercise! You're an adult. Enjoy some of the perks of being able to set boundaries =)