I need opinion. Bub had constipation problem with formula before. I was thinking to change formula because his gas problem doesn't seem to show any improvement. He is 10w now. Today, the nurse suggests to add thickener to help with the reflux. She said no need to add to the full bottle. Just a bit at the beginning of the feed. Does this sound right? We hesitate to change formula because we just don't know the source of the problem.