H.,
I am so sorry you have to return to work so soon. I hated returning to work, too.
A couple of things to consider. First, you are tapping your breasts twice right now - once when you feed your son and then again to pump, so it isn't unusual that your pumped supply is low.
When you return to work, your son won't be nursing, so your pumping will get all of your milk, so you should see larger returns. I think once you return to work, you will find that you pump enough at work to supply your child's bottles the following day.
It's hard to build up a stored supply when your baby feeds on demand, but pumping first thing in the morning would help, because it is when your breasts should be fullest.
If you can build up a 2-3 day supply before you return to work, I think you will find that it is sufficient.
Safe ways to build your milk production other than nursing and pumping include the herb Fenugreek, which you can find in a health food store or Wholefoods. There are also several teas made with it, one is called Mother's Milk. I haven't used them, but I am told that with some sugar and milk, they aren't too bad.
Oatmeal is a natural milk boosting food, so try to eat at least a serving or two a day (and yes, instant, cookies, etc. count).
I have also had luck with guided meditations - see Anjionline.com, and click on the store link. I think the nursing ones are on a CD called A Bond Like No Other, and you can download them instantly. I have found that relaxation is CRITICAL to the process. If I am stressed, my milk will never let down.
Obviously a good pump is also a help.
Good luck,
C.