My daughter had terrible gas and diarrhea from day one. So while I pumped, I mixed half bm to half similac soy and then when I stopped pumping, full soy. She has done GREAT on it ever since. She was 6 lbs 8 oz at birth and now at 5 months is at close to 16 lbs. Her doctor has said that her sensitivity is not genetic after all and we can go to similac sensitive, if we choose, but I tend to believe, if it works, why change. Hope this helps, but if not, good luck with the formula issue.