I know exactly what you are going through. I have a 14 month old that is just barely meeting the 20lb mark. He was a large newborn (weighing in at 8lbs 12oz), but he was also a week overdue. He started to level off in his weight gain around 6 months and fell from the 25th percentile to off the charts completely. My pediatrician has done every type of lab test possible to find out if something is wrong. All tests were negative. He is EXTREMELY active, he never stops! I was also a small baby and my mother told me she went through the same thing- I was skin and bones until my freshman year in highschool! I think it is just an over active metabolism. My son is also a picky eater, which we have struggled with from day 1. He eats until he is full and that is that! I don't force him to eat. He gets 3-4 meals a day with snacks in between. When he was on formula, he never took more than 5-6 oz per feeding. Every child grows and developes diferently. You, as a mom, know when something is truley wrong with your baby. If you are really concerned, then you should bring him back to the Ped. and have them do stool and urine tests to ease your mind. People will have their opinions...and let them have them. At the end of the day, you know what is best!