Thanks for writing.
Yes it could be due ovulatory dysfunction
One of the reasons for ovulation dysfunction
is PCOS which you say you have already ruled out.
The other possibility can be a thyroid disorder
which can also present with irregular light periods. You need to have a serum TSH estimated for this.
If you are over weight, you need to loose weight as it also causes ovulation abnormality.
If you have not got a premenstrual biopsy
done, then you can get it done to know the cause of your delayed period by studying the uterine lining.