S.S.
My daughter had similar problems. She stayed at 15lbs from 6-12months. We monitor her weight very closely and they have run blood tests to rule out any major problems (all they found was that she was slightly anemic). She's two now and still at the extreme bottom of the growth chart, but as long as she stays on the chart we're going to toss it up to genetics. In the beginning we tried increasing her daily calorie intake, mostly by pushing fruits and toddler meat sticks and really anything that she would eat. She's almost 2 1/2 now and has NEVER had a chuncky stage. She's just my little petite princess.