I have not have my period for more than 4 months now?

I havent had my periods for more than 4 months now.....I usually skip lik a month or 2 but never 4....I don't take birth control pills or anything.....Is it healthy?......Does it mean that its done...im in my menopause...I'm 18 by the way...I first got mine lik when I was 11yr....Can it be cause of that?