Tips for tiny babies?

Renee is a bit of a small fry and she is not really gaining weight. She weighed 8lbs when she was born and at her six month checkup today, is only weighing 12lbs, only a four pound gain in six months. She has at least five bottles a day of soy formula and she has veggies or fruit for lunch and dinner, cereal for breakfast. Some days she is hungrier than others. The pediatrician suggested trying to feed her a fruit for breakfast as well and maybe an afternoon snack, the Gerber puff snacks to help with her weight. She is at the 3 percentile for her age.
Any other suggestions?

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    About Christina
    Current: Lebanon, Pennsylvania
    Birth: May 22
    On since: Jul 11, 2014
    I am a mom that works full time from home. I have two beautiful little girls and enjoy every minute that I spend with them.