When my periods were really severely irregular and abnormal due to coming off the pill (this was a couple of years ago), the doctor sent me to have an ultrasound for possible PCOS.  The results showed no cysts on my ovaries but the doctor said "just because there are no cysts, it doesn't mean you don't have it".  Well, 8 years of being off the pill, losing the weight I gained from its effects and such my periods are right as rain and I don't have PCOS.  I really think that PCOS is just the "go to" diagnosis for doctors to explain why women have irregular periods that are actually completely normal for them, because apparently even when there is absolutely no evidence of PCOS you can still have it -_- by virtue of being a bit overweight.  My period goes in a 1 month, 2 month, 3 month cycle (where those are the months between periods before it cycles back again).  Yeah it's weird but it's what it was doing before I was on the pill and using a period tracker I can see the rhythm of my body clearly.  I don't have PCOS, I'm a healthy weight now and it wasn't difficult to lose the weight.  I suspect most of the women with "PCOS" don't actually have it, the doctor probably told them that it's a possibility, even without evidence.  So they just say they have it and use it as an excuse as opposed to actually doing something about it.