Thanks for the replies, everyone. To answer @Beelzybub, yes I was having issues with FPS even playing solo. Though thankfully it seemed to be something weird going on with the game, because last time I played the FPS was back up to an average of about 95. This was after removing 2 of the 4 mods, the ones that added extra items, and that seems to have fixed it for now.
It was just strange because this all originally happened in the middle of me playing, it was perfectly fine before that. I already had like 12 hours of playtime with those mods installed. Guess it was just some insta