Iphone 5s touch freezes

Hello,

I purchased iPhone 5s in January 2015... but now it freezes .. although home button works fine ... its touch screen freezes for few seconds then i lock and unlock then phone then it becomes OK ... what might be the cause ? i know it is generally not a hardware problem .... i though screen protector might be causing this i removed it but still facing the same issue ....

i will highly appreciate your answers in this regard...

thanks