Yup...I second all the other mom's. In fact, I was on the other spectrum, I was the one really worried. Our pediatrician always put me to ease. My 1st son has been in the 5-10% from the get go. In fact, that's why our pediatrician said not to worry. He's on his own curve and that's okay! If there was a drastic change either way...off "his" normal curve then they'd be concerned.
I should note at the 9/12 month check up he did drop in weight that really made me wonder if I was doing something wrong. But the pediatrician said its normal at this stage in development to have a slight decrease, with their desire to explore-- its often difficult to get them to sit down and eat and they're burning all those calories exploring!
Unless your Mommy instinct is telling you otherwise I wouldn't worry about doing extra test. Just in form the pediatrician you'd like to wait a few months and see how things pan out. She's been poked and prodded enough for now :)
Oh ya with the walking thing, my son didn't walk until 15 months. I wouldn't worry about the walking until she's closer to 18 months. She gets around and obviously moves very well crawling, some just don't to bother with changing something their good at :)
Just an FYI my son is now 3 and only weighs 28/29 lbs (my 15 month old weighs 24)! He's still in the 10-15% for height and weight!
Hanging in there you're doing a great job some kids are just smaller than others!