Why does my iphone 5s keep turning off and on unexpectedly?

I've just purchased my iphone over a week ago. It has the latest iOS and all apps are updated.

But recently in the past few days it just restarts. The screen has even turned blue before displaying the Apple logo.

I've also dropped it only 3 times, from a few feet from the ground. Those times it only slipped from my hand, not thrown if that matters.

I've tried hard resetting it multiple times. It happened a moment ago when I tried to download Twitter.

I don't know if I should send my device for repair or if I could fix it myself.