Nothing's changed in my settings or OS, but it does seem to be a wide-spread problem. I'm not sure if it's just on Win7, as my Win10 computer has started having the same problem. I'm updating my drivers as I type this, but it's a slim hope that'll fix the problem.
And I've watched, at least, a dozen or more YouTube videos about the problem, and it's mostly just "update your drivers" or "turn your volume up" kinda things.
I hope it's not a faulty update, and something Microsoft will pay attention to and fix, but, again, slim hope.
I appreciate the help, but it looks like I'm stuck just having low sound.