People originally believed the song was titled "Melodrama", but the concert setlist revealed it was actually titled "Sober (Interlude)". But later, on the track list, it was finally confirmed to be titled "Sober II (Melodrama)". 
Writing and composition
About the song, Lorde said:
"I kind of see these two songs as a big journey of an evening, of a party. I love the idea of Sober [being] the party and Sober II is like ‘the lights are on’. How heartbreaking is it when the lights are on, after you’ve spent however many hours in this dark room and gotten to know it for its darkness? [When] the lights are in, it’s so depressing. You know when you’re loading the dishwasher the morning after a party and everything smells like alcohol and you’re like ‘I could spew, just from these odors’. That’s sort of the DNA of Sober II."She described Sober II by saying:
"That song is interesting, it’s the second part of one of the first songs that we wrote where I really started to understand what the album would be, which was “Sober.” The two of them kind of came around the same time, this was April of last year — I remember Jack [Antonoff] and I went out to Coachella and we got a studio in Palm Springs.
It’s funny, I have synesthesia, which people have asked me about, and the clearest example of synesthesia kicking in with this record was with this song and with the other part, “Sober.” It just, all of a sudden the color of the record was so present and vivid and it was just the craziest — just this sort of rain of violets and blues. And it was so intense, and that sort of came to shape the rest of the record.
So this song sort of maps the course of a party. In the first part, it’s very much like the party’s in full swing, and maybe sort of tipping over into that area where it might be a little too much, and then [“Sober II”] is sort of singing from the perspective of the deflated room. There’s such a sadness to the lights being on after a party, you know, this whole room has sort of been washed in this dark, and to see the corners of the room again can always be a little bit heartbreaking."
Lorde performed "Sober II (Melodrama)" on April 14th at a pre-Coachella gig. It also appears on her setlist for the Melodrama World Tour.