Dear Alice, I have had very regular periods in the last 5 months, which is unusual for me. 8 months ago I took the post-coital pill when the condom broke. Dear Monthlies, The post-coital pill has a side effect for some women of irregularity during the next menstrual period after use, but there should not be long lasting effects 8 months after use.
Any cycle lasting from twenty to thirty six days is considered normal.
A woman's menstrual cycles can change based on diet, stress level, amount of exercise, and other lifestyle changes, such as college vs. home life, having regular sex vs. not.