Baby not gaining enough

Hi Ladies! My LO is 5 months and is pure breastfed. She can take around 5-6 bottles of 150mL of breastmilk from 7-7, when I'm at work. and breastfeed on demand right after. On weekends, i nurse her. She usually wakes once MOTN but can only take around 50-70mL of milk. Just had a doctor's check and she said that the baby's weight and growth is a bit low. 😓 although just a week ago she did had a flu. But the weightlost, if any, wouldnt be that much, right? How do you guys usually do about this? Do you give them any supplements? I thought she was latching/feeding well because her diaper output is usually within 6-8 times per day with 2-4 times of pooping. 😓 Now, i started worrying. Any advice?