Breast milk

How much breast milk are you producing? I only get almost 2 oz altogether every 2-3 hours. I'm just worried cause my son isn't xl gaining weight and I don't want to give him formula! I usually feed him on each side first for about 10-15 mins then pump and feed him what I pump. I pumped yesterday before feeding him to see how much I was actually making and it was 2 oz total. Help!