Do you pump in the middle of the night?

[sailalong]

So my LO is nearly 4wks old and has recently started sleeping up to 6h at night after cluster feeding every 45 min-hour for several hours before the long stretch. The issue with this is that I always seem to wake up engorged after ~3h. Should I be pumping to empty my breasts or just to relieve the engorgement? I'm trying to get my supply up so that I can build up a stash for when I go back to work. The past 2 nights I've tried pumping at 3am and am only getting ~ 3oz total from both breasts which doesn't seem like a lot. I'm worried that if I don't pump then my supply will get even lower? I know he's been getting enough milk over the past 2 weeks as he's gaining weight wonderfully, at his 3 weeks checkup he was over a pound heavier than his birth weight. I just worry that my milk supply won't keep up with his increasing demand over time.