I'm 16
And I haven't had periods since the past two months,
I'm not pregnant
And have been eating well
So what could the reason be?
I'm really worred and concerned

You could always ask your doctor. This could be normal for you, or your period could be adjusting to that annual time schedule. I know several of my friends, who, at that age, had the same thing happen to them, I did too. Ask your doctor what's up, and don't worry.