average BM from pumping exclusively

I'm on 4th week postpartum, currently pumping every 2-3 hourly. total pump each time is about 100mls and baby is taking 80mls now. I'm worried it will soon be insufficient. not sure should I be worried and if 100mls for each pump session is considered low supply? each pump I try to pump 20 mins but I realised usually after the first 10 mins not much coming out. continued for another 10 mins as I heard this helps to stimulate and produce more. but have been doing so since a week ago but amount still the same. sometimes end of the day only able to get 70-80mls per pump. am aware there's no average as it varies for each person but how much do mummies get from each pump? TIA!