I recently switched from the Business guild to the Agricultural guild to a "Cheesemaking" main quest and it's made the grind a lot more interesting. I get to interact with NPCs I hadn't before, such as from the fowl class - "Chicken" and ruminant class - "Goat", and that has opened up a bunch of interesting sidequests, like harvesting useful plants. The world is a lot less dungeon-y now too since I also switched to the "Nature" area of the map from "City". The best part is I recently started a co-op playthrough in "Married" mode with a fellow player who acquired the "Husband" achievement while I acquired the "Wife" achievement. I don't earn as much gold as I used to but I find this quest to be much more fun than when I was on the "Office" main quest.

Don't worry - when I was Level 14, everything was boring too. Your stats aren't high enough, many areas are locked, you can't earn much gold, and you only have a few sidequests to work through while you achieve your "Graduation" primary quest. Try to have fun with the grind! After this it gets a lot more demanding.

I'm Level 28 now and the grind is harder but way more fun. You'll figure out what quest you'd like to do most as you level up - try as many sidequests as you can now to both boost your stats and look for a main quest. "Volunteering" and "Extracurricular" are both good sidequest categories, and you could increase your skills in "Music" (can lead to meeting other players and perhaps joining the "Band" or "Orchestra" guilds), "Foreign Language" (for when you can explore other areas of the map), or "Sports", which will definitely increase your HP.

Good luck and have fun! It's a big world out there, even if other players have already discovered the whole map.