Seemingly random performance drops on Pop!_OS

I am sure many PC users have experienced slow downs on their computers over time (mine is about a year old), but this scenario I find strange. **The Problem** At about 5:30PM yesterday I was browsing the web and running commands (mainly trying to change my background in a shell script). I had a few different web pages open when I noticed huge amounts of lag. I tried closing all windows and nothing changed. I could tell by moving my mouse across the screen that it would freeze for a small period of time every second. I assumed a restart would handle it, but the lag persisted. The next day I started my PC and everything seemed normal, but after opening a few windows the lag started again. I noticed it started and stopped randomly, sometimes happening right when I booted and it would even go away sometimes. This is when I started to try and find the problem. **Possible causes** 1) The last thing I can remember doing before the lag is running # gsettings set org.gnome.desktop.background picture-uri file:///home/jonas/Pictures/dark-wallpaper.jpeg. This command did not work (I was trying to change the background). 2) A bit earlier I tried to install banshee by adding the repository # sudo add-apt-repository ppa:banshee-team/ppa. This threw an error so I removed the repository with the -r option. I also tried to install 'lyrebird' with # sudo dpkg -i lyrebird_1.1.0-3.deb which I had downloaded from Github. Both attempts were unsuccessful. **What I've tried** 1) Run clamscan on my home directory folder (0 viruses detected) 2) Check system monitor for possible resource intensive programs. I compared a screenshot of it when lag wasn't happening and when it was, there were no differences. I doubt anyone will be able to give me an exact cause, but even just a suggestion on how to find the problem will mean a lot.