Don't worry,
My baby also got "yellow" when he was born.
The doctor told me he has never seen a baby with "yellow" like that. My baby needed to do the IV and sleeped under three lights all day. Also, he needed to do the blood test twice everyday.
Stayed in hospital for 10 days, over 20 times of blood test and fianlly dropped to a safe level.
So you don have to worry.