Writing my fic has become boring now that main couple is together

So I'm working on a fic, about 20 chapters. I'm on chapter 17, the couple got together in chapter 16. I know how the story ends but it still needs some fleshing out to get there, and I'm realizing all of the tension between the main couple has been lost now that they're together. Has this happened to anyone and how did you resolve it (if you did?!) I'm thinking of adding some external conflict because it feels too new for them to have conflict within the relationship itself. I can't just keep writing scenes of them making out for 4 chapters lol.