My period is 100 days late

[DaniCaniff1]

I'm 13 years old and started my period 2 years ago (gr 5 and now finishing 7.) My mother doesn't know I've had it yet, and I'm 100 days late. I know for a fact I'm not pregnant because I've never been sexually active. I know when you first start your period they are a irregular but I ALWAYS got mine every month. I'm just scared that something I'd wrong or I may be pregnant. (I know you have to be sexually active and have unprotected Intercourse, but it's a possibility that someone night ducked me even if I don't remember) it may be some stupid thing but id like some options on what it could be.
Please help!