I'm running Blender 2.91.0 (This is a completely new install) and as I use it, it starts to run slower, and the amount of memory it uses according to task manager steadily increases. If I shut down Blender and reopen the same file, everything goes back to how it should run, and eventually it starts to lag. I'm not trying to do any complex rendering, this is a simple low-poly humanoid model with 1 material and basic rigging, and it doesn't appear to matter what I do; I've noticed gradual lag while modelling, editing weights, and animating/working in pose mode. I have also noticed the same issue with other unrigged models.
When I first launch blender, a generic walk animation runs at 24fps, but that steadily drops as low as 14. Memory shouldn't be an issue, as I have 32gb of ram, and Blender only uses around 1 at that fps. Blender is also the only program that lags when this happens - I can run anything else perfectly normally at the same time, and my mouse doesn't lag at all.
I've tried looking this up, but the only things I can find that seem similar are regarding issues with Linux or an Nvidia graphics card (I'm running on Windows 10 with integrated Intel graphics), and specifically while rendering or using custom scripts.