Baby with reflux overeating, can i give him water?

I think the overeating has caused the reflux. He's 4 weeks old and has already gained 2 lbs! The doc told me to give him smaller more frequent feedings to help the pain, but he screams for more when I give him less. Can I give him a little water to satisfy him better. Also would it be OK to give him a couple drops of pepto until the meds the do perscribed start working. I feel awful because he seems to be in a lot of pain. He can't sleep more than ten minutes at a time.