why my CPU running at unstabble frequency and downclocking itself?

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Ansh2236
Ansh2236 Member Posts: 32 Troubleshooter
https://www.userbenchmark.com/UserRun/38496318
here's the benchmark my pc is not performing as expected it is running at very unstable frequency single core turbo of this cpu GHz is 4.5 and when all cores runnig the frequency should be 4GHz but as you can see my benchmark shows its is running on 3.6 GHz sometimes it goes below the base clock and its super annoying when i am playing games like apex legends the frames drops from 120 fps to 45 fps i saw benchmark results of other people with same build everybody is getting 4GHz constanty can somebody help me to get my pc back to 
Thanks for your time .