You should see a doctor about this.  Your periods should be regular by now (mine have always been fairly regular), but they're not.  If your periods are sill irregular, there is probably something wrong.  Remember that some women always have irregular periods for whatever reason, but when they're coming that far apart, something's up, and you should get checked out.

OP here.  Thanks so much for the answer!  My periods do not occur during the same months, although most of them happen around fall.

My mother and I have had the lingering suspicion that I might be intersex, since some intersex people can menstruate.  Since it hasn't impacted my life in a serious manner, I'm going to  put off getting a check up for a while.  However, I definitely want to look into it.

Go to the doctor for a check- up. It may be nothing, but it could be something big. Just wondering, does it always happen on the same month?

 OP here.  For some reason, my description wasn't included with my question, so I'm leaving a copy in the answers:

I'm currently twenty-years-old, and I started my period when I was twelve.  I then had my period when I was fourteen, then sixteen, etc.  Two year gaps between cycles.

I've tried searching for information on the Internet and have found no one else who experiences this.  I'm wondering if I should go get checked up, since it hasn't impacted my life negatively thus far.  Honestly, I'm afraid of having to undergo invasive procedures to find out what's going on with me.

I am physically healthy and at an ideal weight for my height.  The only illness I have (that I know of) is anemia.

I do not think I have PCOS, since I have none of the symptoms other than period irregularity.  The same goes for premature menopause.

Any information is much appreciated.