This could be due to endometriosis, diseases of pituitary gland, hormonal
imbalance of estrogen and progesterone, thyroid
hormone imbalance and cervical infections like cervicitis or cervical dysplasia.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps.