Why is this girl suddenly shy around me?

She’ll act all shy around me and fidget, stare into my eyes when I talk to her and laugh at my jokes. But then other times looks scared of me and run away, then catch her looking at me but hiding it. She acts disinterested sometimes, kind of moody as well but I’m thinking she might be hiding her feelings or something? Or am I overthinking.
Why is this girl suddenly shy around me?
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