After 7.1.2 ios Update, my 5s Iphone Wifi Turn off when screen is locked

I was using iPhone from past 4 months. Everything was all right. But might be with this update of iOS 7.1.2 my wifi goes off when screen is locked.

I can't receive email's neither can receive iMessages nor Facetime Calls..

Everything was perfectly all right before a week but now this is happening...

Please Do help me because i am really suffering from it...