You can find out which app is causing pop-ups on your phone by checking the recent apps list or look for an app without an icon. If you have an Android phone, you can also check the Google Play Store for the last used app: Open the Play Store on your phone and tap the three stacked bars in the top-left corner of your window. Tap My apps & games. Choose the Installed tab, then tap on the sorting icon (the horizontal bar graph next to Last Updated) to select the Last Used sorting method. You should see a list of apps, with the apps most recently used at the top.