Increasing your milk supply!!

HELP!! I really want to continue breastfeeding! I go back to work next week and I'd like to increase my milk supply so that I can stock up for next week. I'm finding that I can't keep up. I pump 5 oz in 20 minutes but my baby feeds about 6 oz so it isn't enough. I breastfeed and wait about 30 minutes to pump and when I do, I pump for 20-30 minutes at least, maybe more. When I'm finished pumping, it's not too long before baby is hungry again and I wouldn't have enough to feed him because I just got finished pumping. HELP! any advice is welcome!