Question Why do I get a choppy gameplay, fps drops and input delay when playing fortnite :( ?

Oct 13, 2020
So here is my build:
i5 3470
gtx1650 oc
16gb ram @1600
seagate HDD
hp stock cpu cooler
hp compaq cmt case (prebuilt)

I play fortnite with that pc. When i initially built it, I was getting really good frames (up to 350fps in creative) and sometimes above 250 midgame. I am aware that in season 4, fps is much lower for everyone, but its really bad for me. I get massive fps drops. Even when my fps is okay (above 100), the gameplay feels choppy, and honestly feels like 40 fps. I have lots of input delay, and feel like everything is really delayed. I get 50fps sometimes in the pre-lobby. I plan on upgrading to an i7 3770, because my cpu is always at 100% usage when i run the game. But even then, im sacred that the drop in performance is linked to something else... even booting windows takes a while, and when i click to even open chrome when i boot it for the first time, it take a long time. It has just been feeling slower :(