Breastfeeding struggles

I've been breastfeeding since day one and it was successful until my baby started eating more and I didn't produce enough. My husband and I started using formula as a supplement after I breastfeed and I pump out the remaining breast milk after. Sometimes I pump out about 50 ml but other times I only get about 15 ml. Does anyone pump after they breastfeed and how much do you usually get? Also, how long do you have your baby breastfeed for each session? I do 10 minutes each breast because that's when baby starts to fall asleep and then I pump for 15 minutes.