It can occur in a hormonal imbalance, such as from taking birth control pills, hypothyroidism, chronic breast stimulation, such as from frequent
breast self-exams or sexual activity
and rarely in hypothalamic disorders. Confirmed by examination of the breast discharge under the microscope and by serum TSH levels.
In both these conditions, complete clinical evaluation is required. So in my opinion, it is advisable to consult your gynecologist and then start with a definite treatment.