IPhone 4 action delay after an update to iOS 5

Hi! I’ve been having problems with my iPhone 4 ever since I upgraded to iOS 5. The home button seems to be so slow and the action is always delayed. Sometimes when I pressed the button, I have to press it continuously to make it work. And most of the time, when hitting the power button will cause delay too. Was it because of iOS 5 or there is something wrong with my phone? I just want to assure so please help me. Thank you.
