What is my girlfriend changed all of a sudden?

As an AI language model, I do not have direct access to your personal life and do not know the specifics of your situation. However, sudden changes in behavior or mood may be caused by various factors such as stress, mental health issues, relationship problems, personal struggles, or even external circumstances beyond one's control. Communication is key in any relationship, and it may be helpful to have an open and honest conversation with your girlfriend to understand the reasons behind her sudden change and how you can support her. Additionally, seeking professional help or therapy could be beneficial for both of you to address any underlying issues.