Have you powered off then back on again since this has started? Also, froze any applications recently?
My guess would be that you have an app that is not working right. I would backup everything I wanted to save (text messages can be backed up with 3rd party apps) and then do a Factory Data Reset and not let the phone reinstall every app. I would reinstall only the apps I absolutely had to have and then see if the problem is still occurring. I would then slowly add the other apps one at a time and allow time to determine whether the problem comes back before I installed the next app. A bit long and drawn out process, but it may help show you the culprit.
Good luck.