Glitch in the game or confusion? Please help!

There's a system progression i'm yet to understand. I had the same issue with bart and i just had to wait, i got it around level 16 i think. Now i'm lvl 31 and i'm yet to have lvl 23 quests, it all depends on how fast you are leveling up i think. Even if quests seems unrelated to you and triggered by completely different characters, in some way you have to wait and do the stuff you have, when you're done new things will unlock.