Avast keeps telling me Driver booster is a virus over and over again. I’ve sent it as a false positive and also supposedly told it twice to put it as an exception, but it continues to flag it up unless I put it in the chest. Why does this exception thing not work? Where do I find a list of exceptions?
What does Avast say, post a screenshot.
Try to restart the Avast shields if the exclusions don’t seem to work, this did the trick for me 
IOBit Driver Booster (free) is, obviously, not a virus but unless they have changed in the last two years it has buttons for installing the paid for version or other IOBit products displayed almost as prominently as the actual function buttons of the driver finder/installer software itself.
AVAST is probably treating it as a PUP (Potentially Unwanted Program) installer, which in effect it is, even if it does do what it it is supposed to do ie, find install/drivers.
The problem here I suspect is that it installs parts of itself in more than one location so I’d guess that unless all those locations are added to the AVAST’s exclusions you will get the problem described.
In particular Driver Booster creates a scheduled task in start up. Check CCleaner > Tools > Startup > Scheduled Tasks and disable or delete any Drive Booster entry there. Typically there will be a skip UAC and maybe a program auto updater* too. Also look for any other Drive Booster entries in CCleaner’s the Context Menu listing.
Even then you might find other IOBit Drive Booster bits running elsewhere too if you use either your task manager or a purpose designed process explorer or the very useful Autoruns program.
*Drive Booster being set up to auto-update by default may well be what AVAST does not like. It was that in particular which made me uninstall Driver Booster completely about two years ago despite the fact it had definitely been useful getting my newly installed PC/OS up and running.
Ironically I did that using IOBit’s own Uninstaller program, another decent tool blighted but not ruined by similar issues.
Install unchecky to catch those unwanted add-ons.