oh dear that doesn't sound good. Welcome to Android central by the way, hope we can get this sorted for you.
Does it only do this when you are on a web browser or within any app? It sounds like you have a app on there that is inserting the ads all by itself. Have you installed any new apps recently?
When I use the Chrome browser websites appear for toiletries; games; etc and when I play music the app store appears at random intervals with installs for games. I haven't added any new apps but I've uninstalled all the most recent apps for about 2 weeks before this started.