Regressing on night sleeping! (vent/advice?)

UGH. We had been doing great, LO would be awake most of the day and asleep most of the night, waking up two to three times a night to nurse but always going right back to sleep.

Fast forward to now.

The last week, baby has totally reversed it. She wakes up at 9pm, ready to play, and stays awake literally all night. Not one blink of sleep. Then 6am hits, and like magic she dozes off into a peaceful sleep. She sleeps for most of the day, and then at 9pm we repeat the horrible cycle.

Even if I try to keep her awake during the day, she still nods right off and throws fits if I try to keep her from falling asleep or wake her up. And at night, if I set her down or try to put her in her bassinet or bouncer or swing, she cries and cries until somebody picks her up. Last night, DH and I took turns with two-hour shifts during the night staying up with her, but even when it wasn't my turn I was still awake because she was wanting to cluster feed and crying her eyes out every time DH tried to put her down. And DH was up while it was my turn becase she just couldn't be calmed down, and because we've got family staying over I had to keep her in our room and the nursery (which is attached to our room), so he was awake listening to us. 

I am so tired. And with family still in town, I can't really "sleep when the baby sleeps" either. The only sleep I get is from about 6am to about 9am. I am running on fumes. I'm beyond fumes. I'm stranded on the side of the road out of gas.

Somebody please help me! I'm losing my mind!!