I have realy low FPS. Help pls :3

When im playing LoL i get low FPS. i start at over 200, 1 second later im on 140 and 5 seconds later on 110. Once i reach lane it goes down to 71-55. And in teamfights past 20 minutes i get less than 30 FPS. My System should be able to pull a few more FPS im sure. At least not 30 fps at 20 minutes.... (Very low and maxed out graphics produce the same Frames) It's unpayable past the early game. Checked my RAM, seems fine. My CPU is running at about 20-30%. My Gpu is brand new and all cables are plugged in and i have the latest Drivers. My specs are: Processor AMD FX-6300 Six-Core Processor @3.5GH   Video Card NVIDIA GeForce GTX 1050 Ti 4Gb OC   RAM 16 GB   Operating System Microsoft Windows 10, 64-bit Power Adapter provides 550w Thank you for your Attention already :3
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