Someone correct me if I'm wrong, but I believe sometimes yeast infections just happen. I know mine wasn't caused by sex.. just one day I was super itchy.

It can also happen if you are on antibiotics.

But don't be scared - just because you tell your mom you have a yeast infection doesn't mean that she's going to assume that you are sexually active. I would highly reccomend going to a doctor, because they can diagnose it, you can go on medication, and it will stop itching.