Hello, I have gone through your query and understand your concern. Yes. It is usual to have irregular periods after taking any hormone containing birth control pills. Prostinar contains levonorgesterol, an progesterone. This is nothing due to worry about. These delay in the period is due to hormonal imbalance caused by exogenous use of levonorgesterol. You will get regular periods shortly after one or two cycles. Until you may have irregular bleeding and spotting. Try to avoid emergency contraception tablets unless in unavoidable situation. Try to have barrier methods of contraception in future. Hope this helps. Please write back for further queries. Wishing you good health.