My iphone won't stay on for more than two minuets?

I updated my iphone to that knew design thingy they just created. It worked fine at first, but than after a day it just would not stay on for more than two minuets (it would go into the recovery apple sign). Its fully charged and I can't think of anything that would cause it to shut down every two minuets. I'm not very smart at this technological stuff, so if anyone knows how to fix this, that would be great.

Take it to the shop. They will be able to pinpoint what is making the phone do this and repair it however needed

Try the settings,

settings --> general-->auto lock.

Change the time that you wish it stay on without going to lock mode