Hello, welcome to the Community, and thanks for reaching out. Have you checked your app drawer for the Camera app, or used the search bar and typed "camera" to see if the Camera app appears?
What is "tweeting"? Did you install any apps recently? Have you installed a theme recently? Is your phone up to date?
Lastly, have you checked your notification settings for texts? Flashing twice for this is a normal setting you can set for texts, but it has to be set by you or an application.
