We just had to switch from similac advance, to enfamil prosobee lipil. My 3 week old son was drinking 4 oz. of similac every 3-4 hours and very rarely spit up. However we had to switch due to his constipation and extreme gas

The soy formula seems to be helping his gas but the problem is that he will only drink 2.5 - 3 oz. of it. It's only been one though (5 bottles so far). Did this happen to anyone?