Regarding periods. Why it's happening.

My periods cycle length is usually 30-31days regu I'm trying to pregnancy too from past 3 months. My AMH is 1.97.my gync prescribed overes plus tablets to support, but it causes me severe acne on my face. So after 1month I stopped that tablets. Then I informed to my gync too. She advised to consult dermatologist. Then dermtlgst 1stly prescribed mild creams.  She told me that, if acne not stops, then come on next my periods 3rd day.acne not stopped. so After 1month again visited dermtlgst on 3rd day of my periods.this time she prescribed a medicine that T. Augmentin 625mg tablet.she Told to take that till 10th day of periods twice a day after meals. I continued same. Then acne decreases. And stopped.ths happened last month cycle. So periods started 3oth day. But this month I noticed that ovulation occurred 8th day of cycle and period started 25th day..why it's happening. I m worry about this.plz tell me