Iphone7 keeps switching off and restarting

Hi, my Iphone7 keeps switching off and then most time switches back on on its own. This has become a regular occurrence multiple times a day and it is extremely tedious. I need a real solution; can anyone help? Would I lose all of my saved setting on the apps (i.e. logins etc) if I back it up and restore factory setting? Any suggestion on how NOT to lose my settings of the current apps?