My LO is 4 weeks & 5 days and I've been having so much trouble finding a formula that is just right for him. At the hospital due to not producing enough milk for a 9 pound 14oz baby they gave him similac advanced which he spit up and got cramps from so they switched him to soy isomil from similac which was nice until almost two weeks later he got constipated and extreme gas pains also notice he was would spit up and eat it and gasp and wheez. So I switched him to enfamil gentlease and that was good until a couple days later he started spitting up 2-3 times after each feeding. So my doctor recommended enfamil AR which hasn't worked at all he projectile vomited the first time I gave it to him and cries and yells in tummy pain.