My phone repeatedly reboots

Hi, my S5 repeatedly reboot like 5 or more times, then if I'm lucky it works for like 2 hours or more but I can't use games apps and sometimes with simple apps like what's app it reboots again, and start doing it again and again, that had happened to me before but the phone stopped doing it like for 1 month and it is doing it again, I'll appreciate your help thanks