Breastfeeding troubles

So I'm a first time mom and I really want to breastfeed only. Problem was that when I brought him home he lost over a pound and doctor said I need to give him bottles because he wasn't getting enough from me. I've been power pumping and drinking a ton of water and latching him on between bottels. What else can I do to boost my supply ? pumping doesn't seem to work I'm barley making anything. Any ideas ?