My ds is has been on Nutramigen AA (the elemental form of Nutramigen) now for about 3 months and is also having a hard time with it. At first things were much better, but over the past few weeks we've been dealing with constipation and gas. Our dietitian suggested trying another elemental formula. So we are switching to Elecare, and if that doesn't work, we'll be going to Neocate. She also said that for some reason some kids have to switch back and forth every couple of months. It's like their bodies build up an immunity to the formula they're on and so you have to switch for a while. Sounds strange to me, but we're giving it a try. Good luck and let me know how it goes!