Low FPS in games despite low GPU/CPU usage

My system:
CPU: AMD FX-6350 @ 3.9Ghz
GPU: AMD Radeon R9 280X
RAM: 8GB DDR3 1600MHz
PSU: Antec HGC-620M 620W
SDD: Crucial 256GB SSD
OS: Windows 7 Professional 64-bit

As the title says. At first I thought it was just my computer not being able to handle the game in questions (dark souls 3), but I checked and saw that my GPU and CPU are barely going above 50% usage despite my low fps <30. I get the same fps regardless of resolution and graphics settings.

I've run a memory test which was fine. Drivers are up to date. I also ran Prime95 which set my CPU usage to 100% so I'm guessing it's not a power issue? I not sure.

I've always struggled to run current and recent games on this machine and I thought it was just because the specs weren't great. Now I'm not sure if that's the case or whether there's something wrong with it.