Kellee ~ Samuel began to lose weight at 4 mths. It was a number of factors that contributed to it. My AF had returned, which the doctors believed changed my milk slightly and he picked up on it....also Samuel started to become a very lazy feeder and wasn't sucking through the hind milk and this effected my milk supply. It took near on a month to work out and explain why (after many tests) he was losing weight and ultimately he went on to formula.....But Phoebe is feeding no differently then what she was a month ago, so I can't really explain the lack of weight gain. I do tend to think that because she has been averaging large weight gains in the past that it just slowed for a little while and will pick up again. (it is a little strange....as I have said before she is so happy and content nothing appears to be wrong..it just doesn't make sense)