JAL,
my daughter only weighted 13.5lb when she was 6 months old, but the doctor didn't say anything. She just belongs to the "small size" baby group. Even the nurse from the health clinic said she is ok.
as for the 濕疹, maybe you can try to change the milk powder like Nestle H.A. 1 Gold.
I remembered 雀雀 was the first one finished the milk (at the hospital) and he was quite good. As long as he is healthy, eat well, sleep well, won't be any problems, don't worry too much ok