Hello! Baby is one year old, weighs 8,800 grams. Thin appetite doesn't…

Hello! Baby is one year old, weighs 8,800 grams. Thin appetite doesn't really force him to eat distractedly so he eats a little bit. We visited a new pediatrician who asked for vitamins to wake up his appetite. The doctor said to have blood tests done from vein, they will take samples. I am worried about weight at this age.