So basically my FPS cant keep a solid 144 in teamfights even when i put my settings all on low. When i put my res at 1920x1080 i get around 100 fps in teamfights and when i put my settings in even lower (1280x720) my fps is still the same, idk what the problem is but when my FPS goes below 100 my game starts to feel rly laggy because of my 144hz.

My specs are: GTX 1050 Ti & i5 3450S