my phone spazzes and randomly does stuff on its own like typing a bunch of random letters, or scrolling up/down a page, or going out of an app. What can be done about that?

I have a 5S and I've had it since december. ever since i got it I've had trouble whit it. It spaces out at random times, types stuff on its own, goes out of applications, scrolls up/down a page etc. This happens almost daily and the only thing I can do about it is lock my phone, go back in, quit all my apps... Along with that now my touch ID has not been working. Although it has started today, I am worried.