Slacker boob.

It seems like my slacker boob isnt regenerating enough milk. I can tell because every feeding my other side always feels engorged. I have used the hakka on both sides while nursing on the other and slacker boob will get out abot 1 1/2 oz where the one that feels engorged all the time will pump out 3-4oz in one feeding. My baby gets frustrated latching onto the slacker. It always feels so soft and saggy. Any tips on how to even out my supply? Eventually i can get baby to latch to slacker side but is causing pain to my nipple where he latches perfectly to the other side. Ive still been nursing alternatively between sides but i noticed after a feeding on slacker i will usually have to latch him to the other side within the hour.