That value at the bottom right of the screen is frame time, not input lag.
Try closing any other programs you have running in the background. Anything your computer doesn't need to have open in order to run properly can be closed one at a time (or all at once). Sometimes antivirus scans or Windows updates can also cause lag, sometimes those are hard to notice simply by closing programs you have open. Basically, just check your task manager.
If you have everything closed and you are still lagging. Try updating or reinstalling your graphics drivers. If they just updated before you started lagging (nvidia released new drivers recently if you have an nvidia gpu) try rolling back a version.