Hi, Menstrual irregularities can occur due to many causes ranging from psychological factors like stress and strain, physiological like changes in sleep, diet, weight, general causes like anemia, thyroid hormonal abnormalities, etc. All these factors by affecting the reproductive hormone levels can lead to irregularity in menstrual cycles. According to your history as you have undergone the stress and strain of surgery that might have led to the fluctuation in the reproductive hormonal levels and led to the withdrawal bleeding. Usually this can spontaneously get corrected in future. If the irregularity persists, better to get evaluated. By clinical examination and investigations like ultrasound, hemoglobin, blood sugar levels and thyroid profile, the possible cause of your problem can be identified and treatment can be taken accordingly. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Sree Gouri S. R., OBGYN