No sex. No period? Vegetarian?

Okay so I'm a bit worried. I've had protected sex before but I have had my period after that and that was several months back. I have not had sex since then. I know I'm not pregnant but I missed my period. Keep in mind I'm 16. I am a vegetarian and I may have low iron could that be the reason why I skipped it? Or could it just be late. I was supposed to have it last week.
No sex. No period? Vegetarian?
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