Long & skinny

I am night and day different from my sister - she was colicky, and I'm easy; she was active and I just like to chill; she cries at strangers while I smile at them; she slept through the night but I wake up 2-3 times. But what we have in common is an official Chen trait: we're both long and skinny "pinheads". My four month checkup showed that I am 24.75" long (50th%), head circumference 40.1 cm (8th %), but only 13 pounds (15th%), which means I only gained 9 ounces in the last month. It is probably because of my colds and genetics, but my doctor wants to check up on me again in 2 weeks while my Mom feeds me more...