Irregular Period After Six Years

Hello ladies :) I have a question concerning my period. I started getting my periods when I was about twelve or thirteen years old. 
I'm now eighteen, and my periods are still very irregular. I've been without a period for 2-3 months several times before (recently). And even when my period is closer to being on track, it's always early or late by at least week or so. 
While I understand periods are usually irregular for the first few years, I feel as though my period should have regulated itself by now. I mean, it's been about six years. 
I'm curious to hear what you all have to think. Is it still normal to have irregular periods after six years? Should I be concerned? I'd love to hear what you have to say before I decide to make a doctors appointment for it. 
(I am not trying to conceive. I am not on any form of birth control. I am sexually active. I use condoms.)