well, there is a 3-month growth spurt, so if they were close to a month early they could be hitting that right about now. would definitely recommend a cluster feed in that case to help them tank up on the extra calories.
also, when you switched to 4-hr EASY, did you adjust their bottles so they got the same amount of milk overall? (know you probably did, but i know it's one of those things that might not have occured to me either!!)
HTH