I started having a problem with decreased milk production after I went back to work. I talked with the midwife at my ob/gyn, and she recommended taking an herbal supplement called fenugreek. I took two pills three times a day. It takes a few days before you start noticing a difference, but it increased my milk production by about 6 oz a day pumping (I was only getting 8 oz prior to the fenugreek). I also think that a lot of it was stress.... I was stressed about the nursing and whether I would be able to produce enough for my son, so that exacerbated the problem. An additional problem for my son was that he would throw up if I gave him a bottle of milk that had been frozen, so even though I had "extra" milk in the freezer, I couldn't give it to him.
Another option the midwife gave me was to take Reglan. You should be able to talk to your ob/gyn about this since it's a prescription. But you take it 4 times a day for one week, then 3 times a day for a week, 2 times a day for a week, and then once a day after that until you need to stop nursing. I haven't had to go that route yet.
My son is now 10 months old, and I've been pumping at work for about 6 months. I've been pumping in the bathroom...there's a little lounge area, and I just turn the chair towards the corner wall. People come in and out, but most don't even notice me there. I've only had one person stare at me like I was crazy or something.
Good luck! Hope this helps!