Hello D.,
My boy is now only 8mos, and is still under weight, at his 6mos check up he was only 12lbs, so they checked his heart, thyroids, etc. He is perfectly healthy, and eats ALL the time, I nurse all the time. He refuses a bottle, or just plays with it. Anyway, the doctor told me to start him on cereals(baby oatmeal,baby rice, or mixed), and it helped! Mix it with formula, breast milk, or even juice. He loves it, just make sure you nurse him before and after, the cereal makes them thirsty, it's like if you were eating oatmeal, without something to drink. My son, eats lots of cereal then I give him some water, and he eats more. Then I nurse him when he's full, and he's out! Sleeps better, gained weight, and my little boy, is starting to stand at 8mos! I think they just have a high metabolism. Good luck. If you need more... email me personally at ____@____.com care,
D.