Hello and Welcome to ‘Ask A Doctor’ service.
I have reviewed your query and here is my advice.
There is no reason why one-off anal sex would cause irregular menses. The irregularity is more likely to be due to the other causes - incidental which would resolve by itself,
contraceptive use, weight fluctuation, the impact of substances used on
liver function, which affects the
metabolism and blood levels of female hormones. If you are worried, then please see a doctor for detailed examination and investigation.
My personal recommendation at this stage would be - a healthy lifestyle (including diet and exercise), avoiding
substance abuse, maintaining a good weight and a menstrual chart that records the date of your period, number of days of bleeding and nature of bleeding. A menstrual chart for 3-6 months will give a clear indication of any irregularity that is persistent and needs attention.
Hope I have answered your query. Let me know if I can assist you further.
Regards,
Dr. Sabina Hussain