Missed Period

I’m 14 and have been fairly regular for almost two years. I’m experiencing PMS symptoms like cramping, mood swings, tender breasts, and acne. I’m 21 days late on a 30-ish day long cycle. I’ve never had sex. The only reasonable explanation that I can think of is stress, but even that has been fairly manageable these days. If anyone has any insight, please let me know. At this point I’m terrified because I’ve googled and googled away and I’m being told that I have a brain tumor or a thyroid issue. Yes I know that googling this stuff doesn’t help anything but I’m really scared so if anyone has any insight, PLEASE help me out! Thank you and stay safe and healthy!!