Anxiety around strangers

My LO has become so anxious around strangers and it makes me so sad. She used to be so happy and smiley at everyone when we were out and about, but recently she just totally shuts down and clings to me to try and hide if anyone looks at her or tries to speak to us when we’re out. I really, really hope it’s some sort of phase cos I’m starting to beat myself up over what I’ve done to make her so painfully shy and untrusting of people.