Hello. A question... We've been on the schedule for four months now, …

Hello. A question... We've been on the schedule for four months now, but my breast has practically stopped feeding in the last two weeks, maybe twice a day. We feed him formula every 2 hours, 120ml each time...and lately he's been spitting up quite a bit. How can we switch him to eating 150ml every 3-4 hours? Has anyone encountered this? He's awake for 1.5 hours during the day and then sleeps. But his nighttime sleep is every 2-3 hours, and he eats well. But we only go to bed at 11-12 pm with him, and wake up fully at 9-10