A few years ago (when I was at my highest weight) I missed February. I took a home pregnancy test, which was negative and got my menses in March.
Then I skipped April. That led me to the gyno to get a urine test, which was negative. And I got my menses in May.
Now I bet you know where this story is going; that's right. I missed June! Grrrr! Back to the doctor, and this time I got a blood test for pregnancy. Still not with child, but at this point they send me for an ultrasound and ran a bunch of blood work.
They never figured out why my menses were so messed up. To this day my cycle is more like every 6 to 8 weeks. I was told by the gynocologist that the home pregnancy tests are (when used properly) as accurate as a blood test, so I just keep a bunch at home and test often.
After a couple of years I went to an endocrinologist because my PCP thinks I may have PCOS. The endocrinologist assures me that losing even 25 pounds will help my menses become more regular. I was trying to lose it before my next appointment with her, but it got moved up to this week so I will simply have to settle for having lost 5 pounds in the last month.
Good luck.