Is there something wrong with my daughter?

My daughter is 14 months old. She started walking at her first birthday party and hasn't stopped since. She said her first word at 7 months, got her first tooth at 6 months, and crawled at 7 1/2 months. She's pretty much average all the way around, except for her growth. She was born at 39 weeks, 5 days, 2 days before her due date. She was 6 pounds, 1 ounce and 19 inches long. She is now 14 months, 17 pounds, 8 ounces and 27 1/2 inches long. According to my calculations, she is under the 3rd percentile for both height and weight. All 3 of the pediatricians I have taken her to said that she just needs to eat more. She currently drinks 32+ ounces of whole milk, anywhere from 2-6 jars of baby/toddler food, 1 PediaSure a day, plus 1 ml of PolyVitamin Supplement drops a day. I feed her as much as she'll eat at each feeding and I only stop when she either spits it back at me or shows disinterest in the food. I am 5'3" and her father is 5'6", and her father was a very small child and so was his half brother. What could possibly be wrong with my daughter?