Thank you for sharing your question with the EmpowHER community.
Yes, Postinor 2 can affect your menstruation. Women can experience a heavier or lighter next period, or a period that is early or late. Which it sounds like you've experienced all the above.
Other common side effects are tiredness, nausea and vomiting. Some patients have also experienced stomach pain, diarrhoea, dizziness, headache, tender breasts, increased vaginal bleeding and skin reactions.
I hope this helps.