[SOLVED] GPU and CPU usage drop along with Memory and Core clocks, causing FPS drops.

[Confectrix]

I'm not sure what this problem is about, so I posted it on here [moved to "Systems" by moderator]
What to do?
I tried:
-updating drivers
-clean installing Windows
-turning off power saving

My GPU and CPU don't overheat. CPU is at 65C and GPU is at 75-80C. I suspect it might be about PSU, HDD or RAM. But I'm not sure. It maybe even bottlenecking, my CPU usages reach 100 sometimes but not frequently. And my RAM usage is around 7 to 7.5 GBs of RAM, so my RAM may be not enough for some games. I have this problems on such games like CoD: Warzone and Star Wars: Battlefront II. FPS is high (100 FPS) but it drops. I looked at other topics like this but I couldn't find a solution. Help me out?

Specs:
R9 380X
İ5 6400
MSI B150M Motherboard
8 GB RAM (Dual Channel)
1TB HDD 7200RPM

Graphs are below.

I wrote it wrong. It's not CPU Speed and Memory Speed.
It's GPU Core Clock and Memory Clock.

 

[rgd1101]

Ram usage?
if it run out of ram, it will use hdd for virtual memory.

and the make and model of the psu

 

[Confectrix]

Ram usage?
if it run out of ram, it will use hdd for virtual memory.

and the make and model of the psu

Everest 750W 80+ Bronze PSU.