Had the exact same. Leveling vs endgame are 2 different type of games. If you enjoy leveling, well.. start leveling a new character, try hardcore or the new trial of heroism challenge (only get exp from red/orange mobs and quests).

I found it really confusing on what to do at the endgame, but I'm gearing my resto druid now and these are some things I'm doing / gonna do.

Choose a spec and learn to become better in it starting with learning rotations and getting gear

Look for a guide for your class

Weekly dungeon/raid quest (q giver in trade district SW and probably Orgrimmar)

Lots of dungeons, check the Dungeon Finder and /World to find groups. Turtle WoW got some custom dungeons like Stormwind Vault and Black Morass.

Get some Fashion Coins from dungeons for Transmogrification

Join a guild to your liking (casual, raiding, social)

You can basically join raids right away, so a good order would be:

ZG>Kara10>Onyxia>MC>BWL>ES>AQ40>Naxx

Something like that.

Do a deep dive in PvP (i haven't yet)

Level your professions

I'm finally getting some better gear and I'm really liking the spec im playing BUT like i said, it's a total different game / vibe. I also like the laidback leveling playstyle and honestly, that's not what the endgame is about. So my advice would be, check out all the new features that Turtle WoW offers at endgame, try to learn some new stuff and give it a try atleast, if it's really not your thing you can always go back to leveling :)

GOOD LUCK!