Slide to Power Off/Screen shots

I have just recently started to have the following problems with my phone:

My iPhone 5s often goes to the “Slide to Power Off” Screen or just simply goes black. The phone often takes screenshots by itself. The ring/silent switch no longer works. I have to use AssistiveTouch to adjust the volume.

I have iOS 9.0.2. It seems this problem occurred with the recent update to 9. There has been no damage to the phone.

Any tips?