IPhone 5s gives me an alert every 5-10 minutes

I get an alert from my Iphone 5s every 5-10 minutes, but when I look at it, there's no call, no voicemail, no message, no notifications at all. I even checked the clock alarms and it was not set. I checked the sound settings, but didn't find anything unusual there. I also checked the other apps to see if there's a notification coming from it. Do you have a suggestion as to what to check? This is really frustrating.
