my pc is messed up

I’m not sure if it’s just fortnite or my whole pc but fortnite is the only game i’ve played since. One day randomly i got on fortnite and my fps was like 60-100 unstable usally i can run about 360 in creative 280 in game i didnt change any settings in fortnite or anything. I tried checking my pc for corrupt files i tried restarting my pc i tried clearing un needed files i have no clue what else to do i might have a virus or something i honestly dont know can someone help me please