The windows installers are still coming up every time windows starts up. The first one will pop up right when the screen that says "Windows is starting up" comes on. I don't know if this information will be useful or not, as I know every system is different and similar symptoms don't necessarily mean the same issue. . .
But my dad, who was the only person I know who opened up the strange email sent from my email address, is experiencing similar problems. The windows installer messages, the balloon popping up saying his anti-virus software is not working (though his, unlike mine, really wasn't active, and he said it would take a few times before he could get it working), and he's also been experiencing some of the other seemingly random things I have. He also said that neither his anti-virus or Malwarebytes was picking anything up. All of the problems started after opening up the email, as all of my problems started around the time it was sent.
Also, I believe Comodo has found whatever problem was messing up my webcam. I was thinking maybe it was just a bug, as the particular webcam has notoriously buggy software. When we tried to uninstall it, it would not uninstall, and when I looked at my firewall log I saw that the camera was accessing the internet MANY times a day and I was not aware of it. I check my firewall log regularly, and that was something I had not seen before.
I found, in the list of quarantined files from Comodo, that there was one that had been in the webcam file. After it was quarantined, my camera started working normally and I was able to uninstall it without any problems.
I just want to keep you updated on the issues that seem to be fixed (for now) vs. the things that are still messing up.