Growth chart - not growing right???

Ok, these stats are according to the WHO percentile chart. Is my baby underweight? Why did his percentile drop so low?
Week 0.
Weight: 42.1%
Height: 96.4%

Week 1.
Weight: 61.8%
Height: 97.7%

Week 4.
Weight: 38.2%
Height: 86.4%

Week 8.
Weight: 15.9%
Height: 50%

Have you talked to your pediatrician about it?

I don't have a pediatrician but he's getting vaccinated on Wednesday so I am going to ask the nurse who checked him out his first week.

Just wanted opinions from other mothers.

try this chart my be helpful for you

http://www.followchilds.com/charts/7/application

First of all those charts are based on FF infants only so if you are breastfeeding your child will very. Second, if your baby is happy and fed I wouldn't worry about it. If they are gaining lbs your babe is fine. I don't like how they lump every child into one category. >.< It scares people and peeves me a bit. Every baby is different.