Having FPS issues with high-end PC

I don't remember exactly when it started, but I know it was by the end of season 8 / pre-season. By each patch my FPS goes lower.

My specs:

GTX 1070 8GB Intel core i7 7700HQ 16GB RAM SSD/HDD

I've tried everything: Changing HD to SSD. Changing configs everywhere (in league, in nvidia, in nvidia profile spec). Hextec Repair Tool Reinstalling bla bla bla

I have a 144hz monitor and I like to play without stutter, the game keeps falling below 100FPS, even if my configs are on LOW or on HIGHEST they remain EXACTLY the same when it comes to FPS. Seeing my task manager I realized that league is not even using 10% of my GPU, it doesn't go higher than 10%, and not higher than 30% of my CPU, and keeps lagging. I don't think it makes sense to run this game LOWER than 100 FPS with everything on low while I can run games like Rust at the highest settings..

it's like league is limited to not use my GPU / CPU.

Can anybody help me, please?