please just check if there is any app causing an interference. You can also try to use it in safe mode to check if it reboots, either you can try to go to a sat to check may be your software is wrong or also there is may be a virus.
On the other hand there is also probably a damage in the battery wich can be solved easily with the warranty, so in this case I recommend you to back up the phone and bring it to the sat.
