How the hell do you WM go to work the next day and be functional and productive when your LO doesn't STTN?
DS goes in spurts of STTN and not STTN. He does neither consistently.
The nights he is up I'm like a freaking zombie the next day and I'm not back to work yet. (I go back in 3 weeks).

Re: working and not STTN
Ditto! It sucks!! For us it is either one or the other or both babies! So we feel like we never catch a break. But I keep telling myself that they will have to sleep someday.
Know that practically every parent with a baby is going through the same thing.
Lots of coffee.
Same here - lots of coffee, and honestly, I've gotten used to it. I find it really funny that before I had a kid, I wanted to DIE at work the next day if I only got like five hours of sleep for whatever reason. Now it's the norm!
DS gets up 1-2x/night to eat - if it's once, I feel fine, if it's twice, I feel more tired, for sure. The few nights that he keeps waking up, I'm exhausted the next day, but I tell myself I'm lucky that those nights are few and far between!
And yes, we're all in the same boat, and I just remind myself of that.
You just survive...seriously. I went back to work at 7 weeks pp and DS still doesn't sttn at 14 months (although fortunately he just wakes 1-2 x now).
Lots of coffee!