I have a 4 not a 4s but are you using the iphones native camera or a camera app from the app store? I've had trouble with the native camera before and just switched to one of my camera apps and didnt have the problem.
Have you tried that? I recommend Camera+ its free in the app store and awesome.
It might be that one of the plastic pieces that lines the camera might've fallen a little out of place and is reflecting your flash. Or, it could be that your case or screen protector isn't light friendly.