You can try moving him up but if he is not keeping it down or spitting it up you really shouldn't force it. Mine is on a gentle formula too and she is 2 months and is at 4oz. My first was a boy and he drank 8oz by the time he was 2 months so it just shows you how different kids are. According to my pediatrician who by the way has no kids of his own says that kids should not be at 3oz till around 4-6 weeks and then move up gradually because he said if you overfeed a baby they can get an infection in their stomach. Yeah whatever I know he has the degree but children are different and if my kids are hungry I feed them. I would slowly increase him by 1/2oz if you think he is ready and see if he can hold it down if he does great if not scale it back and try it again on a different day. Boys in my experience are big eaters at least mine was just go with your instinct I moved my daughter up to 4oz before I was supposed to but now she goes the full 3 hours before eating and it makes the nights more enjoyable and if she doesn't finish it all who cares at least she isn't hungry.

We have tried Enfamil sensitive and Similac Sensitive as well and it seemed like he was never getting satisfied so we switched to the Enfamil Infant and have been on that ever sense. Its just fine for our little man. But then again, every baby is different. I agree with the above.