Share your experience!
Boot your phone in safe mode,see how it goes:
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008#U348008
Are you using any task killers?Battery savers?I think it is best if you visit a sony service:
http://www.sonymobile.com/global-en/support/contact-us/
Did you get your phone from Bell?Visit their service or a sony service.
If you still have warranty,visit a service(if you have warranty for sony,take it to them).