Hi S.,
I'm gonna give you a couple ideas. I think they all coincide together. So here is where you could start...
* Diet~ portion control, watch the size of the portion you put on your plate, I've always heard that a portion to "you" should be the size of your hand. Also don't stuff yourself only for what satisfies you.
Should you look at what you eat probably but with a controled portion and amount I believe you will loose pounds you want to.
Also when you eat ask yourself am I hungry or just board, angry, upset, stressed out, identify the issue and talk it out. Or when you have the urge to eat something exercise instead say you can only have that candy bar if you do 25 sit-ups, 2 sets. Set yourself a goal and call a friend when you have the urge to give up.
Backpain~ Even a little bit of weight can effect each person.I think that if you got your weight down your back would feel better. Also make sure you are lifting your son correctly, carrying your bags correctly, to not cause your back harm.
Exercise~ This one can be simple and it doesn't require you to go to the gym at all. So first Whe you are going to work park farther away from the building (walking is exercise) if you have to take the elevator, don't take the stairs for now on (this is a good cardio work out and for your lower body strength, your calves and thighs), when you go to class take the longer way to the class room. If you have stairs at home let say you have to run up and down them to go do laundry or to go upstairs whatever the case is do 2 sets of 25. You can add in exercise everywhere you don't have to just go to a gym. If you don't have hand weights use a can of vegetables (you never cook the veggies first) do 3 sets of 10. And on more thing when you and your son are at home turn up the radio and dance around the house, do sit-ups with him sitting on your stomach,20 lbs of baby is a good weight. You can do all kinds of exercises with your son :), use your imagination he will love it and so will you, lol. Take your son for a walk in the stroller 1 night a week.
Stress~ I think your stress is caused by all the things listed above, so when you get home take out your stress notebook and write everything down that you are stressed about, or on the drive home from work or to school say it out loud what you are stressed about. When you finally see your little girl tell her about your day good or bad, she doesn't care what or who you are talking about, she only cares that her mommy is home and is seeing her now.
And one thing to remember always is life is to short so don't sweat the small stuff and what you don't get done today will be there tomorrow. And the most important thing is spend every moment with your baby girl. She can sense your stress and it doesn't do anything for the both of you.
I don't think you need a pill or medication you just need to revaluate what is going on around you. Goodluck W..