FPS Drops Please Help (AMD)

Particularly during big fights, my FPS drops from 144 to anywhere from 50 all the way down to 30, and it’s making Overwatch unplayable.

My PC isn’t great; it was pretty haphazardly built, but from what I understand, Overwatch is supposed to run fine on even lower-end gaming computers. I never had this problem on my old gaming laptop.

My graphics card on this PC is a Radeon RX570 with 4090mb RAM, and my processor is an Intel i5-3470 with 16gb RAM. I’ve updated all my drivers, and I play Overwatch with the lowest graphics settings. I never have programs running in the background.

I find AMD and its software less straightforward than NVIDIA so maybe there is something I’m doing wrong that is easily fixed, or perhaps my hardware is just not great. Would appreciate some advice.

EDIT: Just checked the AMD software and it reckons my average FPS on Overwatch is 56 which is abysmal.

Are the storage drives more than 85% full? Are you overheating?