First thing: are these apps or just shortcut icons on the desktop? They sound more like the latter to me.
Either way it's probably that you've downloaded and installed something dodgy, but how you'd trace it might depend on what it is. If these things are actual apps rather than shortcuts (so you can see them in Setting > Apps or in the app drawer) then you need something capable of scanning app permissions (e.g. Addons Detector, or many security apps - MalwareBytes may be able to) and look for any app that has the permissions to install other apps.
It may be as simple as your web browser has got infected with some adware (if your browser can place shortcuts on the desktop and some script is taking advantage of that). Try clearing your browsers' cache, and be suspicious of any add-ons you added shortly before this started.
If that doesn't fix it, any app you installed or updated shortly before this started is a suspect. And stuff you install from sources other than the Play Store (or Amazon app store, of F-Droid) is more likely to be an issue than stuff installed from known and trusted sources. A few years ago there was a type of advertising code that could put shortcuts on the website, but it has been banned from the Play Store, (Airpush or push notifications, was what it was called). However, it might still exist elsewhere, so if you've been installing from other sources this is something else to consider.
