Low fps even on low settings?

[Zlurz]

So its been 2 weeks since i built my first rig for myself, i chose an Athlon x4 750k as i knew i needed a quad core for gaming but i couldn't afford an i5, for the graphics card i chose a R9 270 2GB from HSI but so far i've had poop performance. I try to play arma 3 at 1080p with everything set to low even having all AA turned off and i still manage to only pull off 20-27 fps which is unplayable since arma frame rates tend to fluctuate quite alot. Is there something wrong with my build? I dont expect my rig to max out at 1080p on ultra, its a midrange card so it would make sense that i could achieve 50fps or more on medium settings, hell even at low settings i should be pulling at least 60+ any thoughts on this? I've already downloaded the most recent drivers so that cant be an issue. Here are my specs.

Athlon X4 750k
HSI R9 270 2GB
8GB ddr3 @ 1600
1TB HDD
EVGA 600w 80+ bronze PSU

I honestly don't know what the issue is, i don't multitask while playing games and i dont run my second monitor either, is my pc just garbage?

 

[BradleyJames]

you should be getting higher fps, especially on low settings. have you tried other games? how do they work?

 

[Seeking Solace]

In my very novice view, it could be the temperature of your system (AMD cpus can run hot and I read mixed reviews for the stock cooler with yours) or possibly the GPU struggling with the resolution (though I really don't know about that)
I've read posts from realchaos that you can download HWMonitor to show your system temps. If it is indeed that.