According to my previous doctor, you should
not go more than 3 months without a period. This puts you at risk for endometrial hyperplasia; which can lead to cancer. (P.S. I had to stop seeing him because of the long drive.)
But, anyway, it's important that you have a menstrual cycle.
(If you go more than 3 months without a period and do it quite frequently, I would suggest you get a transvaginal ultrasound done. This will also check your endometrial lining. If it is too thick, the doctor will do a D&C, I believe. Check with your doctor.
But, above all else, get an endometrial biopsy done. This will tell you, for sure, if you have any issues; including anything pre-cancerous OR cancerous.
In any case, some symptoms of PCOS are irregular or no menstrual periods and there may be an excess production of male hormones (hyperandrogenism); both of which are a direct result of abnormal ovarian function. The exact etiology of PCOS is unknown. A genetic component can be identified in many patients.
So, its important to get bloodwork done.
Check out my previous doctors website. It's helped me out quite a bit. (BTW, he's one of the nations leading experts in PCOS.)
http://www.pcosinformation.com/index.html