My 11 week old has changed her habits too. She is taking her normal 6oz every 3 hrs or so during the day and has gone from sleeping 5-6 hrs to back to being up every 3 hours at night, taking 3 or 4 oz. I think it's just something they may be going through. I told her last night- I thought we were over this newborn nonsense...she just laughed at me. I'm glad she thinks it's funny ;)