I have PCOS, so I've never had normal periods. My husband and I thought we couldn't conceive since we went for 5 years without using any birth control. After I lost 50 lbs. in 1996, I became pregnant. My weight ballooned to 215 during my pregnancy. Over the years, I added 30 more pounds. Once my weight hit 245, I went from having a period every 2 or 3 months to every 6 to 9 months.
Now that I've lost almost 70 lbs., I have had a period every month for the last eight months.

I would second what everyone else has said: See a doctor. I can't tell you what a relief it was to have a name for what was wrong with me.