i was really worried about that too when i was around your age. it feels like all your friends are getting theirs and you're just waiting and waiting.
i promise you're not weird if you haven't got it yet - lots of girls don't get their period till they're 13 or even 14.
try not to stress too much about it, and maybe talk to your mum or a trusted adult about how you're feeling, they can help you figure out what's going on and you'll get through this together.