mama I feel your pain. Well have lived through it. Things to try:
1. someone told me that body position can make a difference when pumping -- meaning if you're leaning on the flanges you sometimes get less milk.
2. pump more often for fewer minutes -- instead of 2 20 mins sessions, try for 3-4 shorter one.
3. drink water, drink water drink water. not thirsty? drink some more.
4. have your childcare provider give your son milk in smaller bottles -- My husband and dcp would give my daughter 2 bottles with 2 ounces instead of 1 4 ounce bottle. Once she got used to sucking it was the sucking she was wanting, not necessarily more milk.
5. try pumping at the same time every day
6. you didn't say what kind of pump you have? if it is something like a pump in style -- tubing comes off, try adjusting the tubing. also try adjusting the pressure.
7. I think LLL recommends breast massage -- www.breastfeeding.com
might have something on that.
and finally, and perhaps most importantly (and advice i wish I had been given). Added stress in your family can be a problem for making enough milk. If you're stressed out over it, then you can't pump as much and then you don't have enough...yada yada yada. I didn't supplement but was constantly pumping and worrying about did i have enough milk. I took a rx for increasing my milk supply, we finally introduced solids at 4.5 months because she just wasn't gaining weight. She's now a healthy 16 month old. If I had to do it over again: I'd supplement with a bottle mixed half BM and half formula. I was a stressed out nightmare, trying to be a good mom. I now know that my body just doesn't pump milk (and maybe doesn't make enough milk) like the best of them. I would have been SUCH a better mom if i had relaxed and just supplemented. For kiddo #2 (if there is one and if it is necessary) I'm sure I will supplement - a few ounces a day, never while I am home.
I hope someone else has more ideas if these don't work. You are doing great things for your baby -- keep up the good work!
one more....working mother nursing mother -- the book -- is a useful reference.