>>>My computer was fine until recently so it can't be a clash in av's.
It probably is a clash of AVs.
When you have two or more security products on your computer they "compete" with each other to check files and this constant checking can slow your computer down.
Here is a McAfee removal tool which will remove all (or most) McAfee products from your computer.
https://service.mcafee.com/FAQDocument.aspx?id=TS101331
Run this, then do a reboot.
Some versions of Windows have a thing called the Action Centre which will tell you what security you have on your PC.
Open the Action Centre and see what security software Windows THINKS you are running.
p.s. It does help if you tell us what version of Windows you are running.
p.p.s It does not help to get paranoid in thinking McAfee are deliberately slowing down your computer (and opening themselves up to a lawsuit) when the real problem is that you did not uninstall McAfee properly.