Increasing supply

My baby is 5 1/2 months old now and only drinks breastmilk. I work 8-5 and pump three times for about 20 min at a time everyday. Lo has refused to nurse during the day for several months now, since he's been at daycare and finds a bottle much easier to eat from. He won't even attempt to latch anymore other than at night. He nurses very well at night. Anyways, He drinks 4 oz every 2.5-3 hrs. It's taken a lot of hard work but I've managed to pump enough milk a day to keep up with what he drinks each day. My job makes if very difficult for me to maintain a regular schedule daily. I try to stick to it as bet i can but sometimes it's just impossible. How do I increase my milk supply when Lo starts wanting to eat more. He seems to be wanting closer to 5 oz now and I just don't pump enough. i do have a freezer stash that he eats from but He's drinking more milk than i'm freezing and at this rate He's going to run out of the freezer stash. He hasn't started on solids yet so maybe once he starts solids he won't demand as much milk. So, How do I increase my supply to meet his needs now? I do alot of pumping on the weekends when I'm at home. Hope this makes sense. Thank you