I exclusively pumped with my DD, exactly what you are describing is what happened to me. I tried all natural known supply boosters first (fenugreek, lactation cookies, etc) and nothing really helped, so my doctor gave me a prescription for Motilium which helped immensely. The gp you saw must have been a bit of a nuff nuff if she didn't know about Motilium. I still ended up having to comp feed with formula, but at least I could get 100ml per boob every 4-5 hours. The problem is is that the pump does not stimulate the breast to produce milk like a baby would, so it's normal for your supply to drop after awhile. Go back to any gp and ask for a prescription for Motilium - if you wait another week you may find you have almost no supply left by then.