iTunes 12.2 update issues in App Store

The App Store on my Macbook Air is not updating any of the apps nor bringing up the latest iTunes 12.2 update. GarageBand and iMovie are trying to update, but it keeps getting stuck and nothing happens; the iTunes update keeps telling me it's available in iTunes, but it doesn't show up in the App Store. If I quit App Store and reopen it to refresh it, nothing happens at all: no GarageBand and iMovie updates, no ability to click on anything, nothing...it is effectively frozen and unresponsive. Anyone have any ideas about how I can unblock the updates and help me download the iTunes update? Thanks