Yeah I realise I'm in a very rosy period right now so my input is skewed!
However I entered into the "now what?" phase with a couple of other boyfriends around the 18mo/2yr mark, so I think you've done well
Part of it might be because you're still pretty young and so maybe haven't really been financially independent for long enough (complete guesswork here, feel free to correct), that the next 'phase' of moving in together, creating a home, and seeing a new dynamic between you and her hasn't happened in what might be the usual time-span, so you're kind of treading water atm.
As soon as that happens activity explodes for a bit - furniture finding, getting used to sharing a bed every night (wahey!), all the domestic stuff now you suddenly do with each other instead of parents, etc. Probably lots bickering and making-up (wahey! again)... Then I guess you settle into a new kind of life where you're guaranteed to see each other - so you'll make an effort now and again but it doesn't have to be a case of "what shall we do now to make the most of time spent together?" any more.
Still doesn't solve your problem now, though. I guess as long as you recognise the above and keep making effort, you'll see it through.
Have a bit of a brainstorming session of making really silly suggestions of things to do - outrageous as you like - they might all end up impractical as hell but will probably spark off some more feasible ideas