I have a 5 week old. When he was born, they started him on Similac Advanced. He started becoming constipated, gassy, and fussy. He also was spitting up and projectile vomiting every now and then. I switched him to Similac Sensitive. He is doing better but he still gets a bit constipated and fussy because he can't get the gas out. I use Gas X and it helps some, and I give him enemas but he gets constipated about every 3 days or so. He still spits up and vomits, just not near as bad. I'm trying to see if any of you may have any other suggestions on another type of formula I could feed him that would help with these problems... I am taking him to the peditrician tomorrow for the reflux problem he may have. Thanks in advance for the advice!