Movie about doppelgangers?

I need help figuring out the name of this movie. I don't remember all of it only some parts. There is this woman I think she might be a doctor or something. Apparently the doppelgangers are trying to take over or something like that. I think she might of had amnesia. She is trying to stop the doppelgangers or something like that. Then she realizes that she is the doppelganger. There is some kind of mirror world where everything is the opposite. If the person is good then the other is bad. I think that's the movie was about. Please help I've been trying to figure out for days!