Dear Icecube,
Much much easier said than done, but try not to stress tooo much over it. Our daughter was born about 50 percentile but she always had a very small appetite. I don't remember the specifics exactly by month but even later on it would be a good day for her if she would have 18-20 oz.
We were really stressed because she wasn't putting on much weight and her weight percentile kept dropping and eventually fell off the chart (below 3%). Our doctor told us repeatedly as long as she was active, happy, and healthy not to worry about it (it lowered the stress a little bit but not much).
Well, now she is 2 years old, still doesn't eat much - hates milk, still is around 3% percentile in weight, but she is healthy, happy, active, smart, and talking non stop.
Sometimes I still stress about how little she eats but there was a recent study that said fat babies turn into fat adults so from a long term perspective its probably a good thing she is petite.