Breast milk

Will my milk increase as baby gets older? I’m exclusively pumping but I’m still not getting how much I would like to. I’m getting different oz at different times.. I pump mostly 1oz each breast. If I’m lucky I rarely get 3-4 oz in one sitting.. I don’t want my milk to dry up. My baby is three weeks old today. I try to pump every 3 hours but sometimes get busy and forget is that why? I try to pump til empty but my breast never fill up.. doesn’t even seem like there is any