phone turning its self off

[sfilansno1fan]

hi i have the galaxy s3 and today it has been really weird it turned its self off and back on again and then a few hours after i took it out my bag to find the notification light on and not flashing it was blue and the screen would not come on i had to pull the it battery out to get it to restart i plugged it into my pc and there was a software update avaliable so i done that and after i did it turned its self off again and by 2pm by battery was down to 45%
normally my battery lasts until at least 10pm if not later
im really confused as ive had my s3 since october last year and ive not had any issues until now
would be greatful if someone could help ?
thanks

 

[meyerweb#CB]

I think a factory reset is in your future, but first:

Have installed any new apps recently? If so, start by uninstalling those and rebooting.

 

[sfilansno1fan]

ive not installed any new apps recently i went onto my latop and using kies i re installed my software
it seems ok at the moment
thanks