Lumia 820 empty in hours

Hey,

I had my Lumia 820 for a while. And it's never really been this bad. My battery life is insane! At one point it was discharging at 30%/hour.

I use my phone a lot, even constantly maybe, but by now it's permanently on low brightness because I'm just too scared of it draining fast. It's not very enjoyable, I want to be able to turn my screen on high sometimes.

Does anyone know what causes this? I've already uninstalled my battery monitoring app because somebody told me they drain too..