Take a break. It'll give you perspective, and more importantly, fill up your rested exp bonus bar. Between that and food ((and those exp manuals for DoL and DoH)) you get a pretty hefty bonus. Then Pull enemies from non-Boss, non-Guard FATES to the edge they aren't reinforcing from. It is currently working for me ((Similar issues with Duty finder, and I generally avoid Leves anyways.)) Took me a few hours up to an afternoon to go from 25-30 on one of my classes.

Alternatively, Make friends and get help, Or get help from friends you already have. I can't attest to this personally, since even in an MMO I am a loner at heart, But I hear good things.