Breastmilk

Need advice how should I increase my breastmilk again.. Last time pump 120ml now become 20-40ml.. I only pump 1 or 2 a day as work related that I can't pump every 2 hrs even my breast feel pain I tahan not to pump thats why milk getting lesser.. Now I no work back to pump milk but to muly dismay not much milk.. Or breast stop producing