Menstrual cycle trouble due to Acne Medicines

Patient: Hello I’m 20years old having face and back acne.Under consultancy of a deramtologist I used Isotroin 5mg and Isoin 20mg , when I got disturbance of my menstrual cycle the dosage was continued for 3 week, in the next term I was given a Iren 20mg and Isotroin 5mg and again I got my cycle within 15days,consulting doctor I was informed that these medicines donot affect my cycle . What to do? I have a lot of acne and this was the first time to get disturbance in my cycle ?