Weight Loss in a 6 week baby

Hi, I went to the clinic today and got the weight of my 6 week baby boy measured which came out to be 4.56 kg. 10 days back, his weight was measured in the same clinic as 4.73 kg. His birth weight was 2.7 kg. He is currently on breastfeed. Even though the doctor says, there could be fluctuations in weight but still I'm worried if he is getting enough feed. The internet says that the baby should gain 30 g every day then why is my baby lost approx 150 g in 10 days!! Anybody has been in my shoes?