Timeline completely lags when I import items, but when I remove items it becomes normal again

Hi, everyone, I've been having this issue recently with Premiere that I can't seem to find a single solution for. 

Things work normally when I import up to 3 items into Premiere, but for some reason when I import another item, the timeline just proceeds to lag in an unexplainable way. The playbacks work normally, everything else in the software works normally, but for some reason the timeline becomes unresponsive. It's not that the software is frozen, either.

When I try to click on the timeline, nothing really moves around. When I try to switch to another sequence, it doesn't do anything. When I try to click on a different part of the timeline to play a different part of the footage, it doesn't move, but if I press the space button, the playback cursor jumps to that part of the timeline and proceeds to continue playing the video. When I try to zoom in/out the timeline, it doesn't actually move or do anything. The timeline becomes weirdly unresponsive and makes editing near impossible.

However, when I remove the items that made the software lag (and the items can be anything, whether that's footage, a new sequence, even a small audio file), the timeline goes back to being completely normal and smooth. However, I try to import another item, and the timeline just completely freezes up again. 

I have no idea what's happening and I've tried searching everywhere for a solution to no avail. Does anyone have any experience with this? It's extremely frustrating and I can't find any solution anywhere because I don't even know what the actual problem is. Thank you.