I've worked on the system that if Eden drains her bottles for more than 3 days in a row, I up the amount of formula - if she leaves a little in her bottle, I know she's full, whereas if she drains it for all I know she could want more? You might find that if you up the amount of food he has, he'll go a little further between feeds. I think Eden was feeding between 3 and 4 hours when she started formula just after 2 weeks. I do seem to remember reading there's a 2 week growth spurt somewhere... xx