Girlfriend is suddenly upset at me and says she didn’t like me (in like a non serious way) and says that it’s all my fault, what can I do?

Extra information: I ask what’s wrong and she won’t respond, she is upset the whole day that we’ve been out and is very not affectionate like before. I don’t know who to ask but I thought here would be a good idea. I appreciate all help

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Update: she is not on her period, it’s either near the end of the month of early start of the month
Girlfriend is suddenly upset at me and says she didn’t like me (in like a non serious way) and says that it’s all my fault, what can I do?
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