@Sarajit
Start troubleshooting by restarting your phone into safe mode, this will disable all installed 3rd party apps. If the problem is resolved then one of your installed apps is causing this issue and you have to figure out which one. Start by uninstalling those apps you installed recently.
If that didn't help, then I'd suggest that you perform a software repair using Xperia Companion. This will do a clean installation of the latest firmware and will also wipe your internal memory. Don't forget to backup using Xperia Companion, but preferably without adding apps or settings to the backup.
For repairs and maintenance, kindly contact your Local support and ask them about how to submit your phone for physical repair.
Follow the steps given in blue links, and keep us updated.
