What do I do now?

[Zahak]

You should check out the Adventurers Guild. You can accept 8 leve quests at a time, take them to the specified camp, and complete their objectives after activating them at the camps Aertheryite Crystal. It's a decent way to solo experience. Also Paladin is a advanced version of Gladiator, by doing the paladin quests you will unlock gear and abilities to further enhance paladin. It's mostly used for group situations though.

[Deubion]

^ Leves. There are also behests which are initiated from "Battlewarden" npcs at the various camps. You can solo them at the appropriate levels. After you get to around 30-35, there should be xp parties every once in awhile looking for members in town; alternatively, you can build your own party using the "search" function, which is easy enough to figure out.

Honestly, it's been years since I did the main story quests, so I don't know which levels you can do them at. I'd say check back with the NPC at your adventurer's guild every 5-10 levels to make sure you get the best xp. They used to give you a pretty hefty sum of gil as well, not sure if that's changed.