Why do my apps and my phone keep shutting off

Ive recently updated my phone and ever since then when im using an app it just shuts off out of the blue. It especially does it on my facebook app but it does it on some of the other ones to. I tried deleting and reinstalling the facebook app but it didnt fix the problem so i haven done that with any o the other apps the shut off. Also since i updated my phone, my phone has shut off randomly out of the blue. I was taking a picture the other day it it just shut off. When i tried to turn it back on it came up with that symbol to charge it. I did so and then i turned it back on and my phone had a 56 percent charge... Weird.

Why is it acting so stupid?