I haven't had a period in 6 months. My diet hasn't changed, I'm getting plenty of calcium, I didn't lose/gain weight, have sex, changed my exercise regime, or anything. My first one was a year and a half ago, and was just brown discharge. The next one 8 months later was also a really small amount, and the next one came extremely heavily 4 months later.
After that I had 2 more extremely heavy periods (leaking through pads every hour), and they all took more than a week including weaning off. The next one after that had a normal amount but wasn't consistent in the days, and that was it. After that I had the occasional blood spots, and that's been it.

I'm not on any medication, don't do drugs, don't drink, don't smoke, and haven't been under any stress.

I am a guy checking the recent posts and saw yours, I had a girlfriend that only had her period usually twice a year, not at a regular interval either, she was over 30 and had always been that way. Some folks on this site are going to advise you go see your GYN so that is a general recommendation, I will just say that it may be a natural occurrence but to be safe, go see the professionals please. You are not alone and I am sure there is a medical term for your condition, probably unpronouncable.

Have you been to the doctor? If not, you certainly need to there could be many many reasons for this but it will take a complete history, physical, and lab work to find out what it is.

I would see a doctor if I were you. A physical should be done and he/she might put you on birth control to help you become regular.