A lot of programs are unusually slow and/or lag immensely

I first noticed this when I booted up uTorrent (for the most legal of purposes, I assure you). The program popped up, a couple lines of text started to display, and then my entire computer started crawling at a snail's pace. uTorrent froze, giving me a (Not Responding) message, and I could only remove it with the Task Manager. After that, things went better, but I noticed it was happening on other programs: I tried downloading a replacement for uTorrent, but the exact same thing occurred; Steam starts to get jittery when I switch between tabs; iTunes takes forever to load, but doesn't display the (Not Responding) and is otherwise normal; the Windows Media Player barely even works, taking forever to even start the song, constantly pausing during it, being unwilling to be closed normally, and slowing my computer down a ton; Chrome randomly jumps between working as usual and not working at all; and so on and so forth. Yes, I have run a virus scanner (two, in fact: Malwarebytes and Avast), and nothing's changed. Any ideas?

use bittorrent

also maybe your cpu is overheating, use http://www.alcpu.com/CoreTemp/ this program to test (assuming you use windows)