I wouldn't worry too much either as others have said...he's eating and seems healthy..and happy, what more could a person ask for! My oldest when she was a baby was pretty small...born a normal weight, 7 lb. 14 oz. and 19 in. long (very normal) but she didn't grow seemingly fast enough for the doctors and kinda kept her "own" growth chart (according to the pedi), well eventually they had me take her to Children's Hospital to be checked out...all for not! I kept trying to tell them she was happy, healthy, eating well, she was just SMALL...she started kindergarten at 30 lbs....she was always smaller than the other kids, but still happy, healthy, and eating well...then when my son was born...same way...8 lb. 2 1/2 oz. and 19" long (perfectly normal) and when he was about the same age as your little guy...they wanted to send him to Children's Hospital for more indepth testing! I told them "no" I wasn't going to go through that all over again as I'd already done that with my first daughter and there were no problems...my oldest daughter is now 22, been married 3 years and is still small, my son, @ 19 is 5'9" and 130 lbs. my next two (twins) are small (weight-wise) son is nearly 17 and 5'8" and 125 lbs. and his twin, she is only 5 feet tall....Alll are healthy and happy and eat well...it's just in the genes!!!! Don't worry, be happy and enjoy your little one!