Baby’s appetite - something I should worry about?

My 7 week old baby’s appetite seems to be steadily decreasing, and she is currently only consuming 400-500ml of milk per day (mixed feeding). This is below the recommended 650ml per day for her weight (4.2kg). Previously she could drink up to 700ml per day and even hit 800ml. Nowadays when I try to feed her more but she either just keeps her mouth firmly shut or seems to want to gag if I force her further. She otherwise usually just sleeps. Is this normal and should I be worried about the amount of milk intake?