I have been creating quizzes & some of them aren't there any more. Why are they going away? And can I get them back?

They are being deleted because they are duplicate questions. I have left comments for you letting you know they are duplicates. There is a "search club" option near the top of the page where you can check to see if a question has already been asked before you post it. People who have been doing this trivia for awhile get really tired of questions that are asked over and over and report them to be deleted. Hope this answers your question.