because it just does.
The average menstrual cycles lasts 28 days - but different women may experience different menstrual cycle lengths, and cycles can change throughout a woman's life.
No, reptiles do not have menstrual cycles or periods like mammals do. Instead, they have reproductive cycles that are different from those of mammals.
No
Yes, your menstrual cycle will change whenever you've been pregnant - whether that pregnancy ends in abortion, miscarriage, or childbirth. It takes time for your cycles to return to normal after pregnancy, it can take up to a year for the cycles to regulate fully again.
No, bearded dragons do not have menstrual cycles. They do not menstruate like humans or some other mammals.
No.
Menstrual cycles aren't a calculation, it's really just as simple as counting from the first day of your period up until the next period. You figure out the average over your last six cycles - anything up to a weeks variation from your average menstrual cycle is considered normal - but cycles can change, it's sometimes easier to use a menstrual tracking app on your phone to keep track for you.
Delayed menstrual cycles have been reported when taking Ciprofloxacin. The delay can also be caused by the urinary tract infection. Both can cause delayed menstrual cycles.
Once a month
You were five days later than you predicted - this prediction was based on your average menstrual cycle length, but menstrual cycles change and they will not be exactly the same throughout your entire life. Anything up to a weeks variation from your average menstrual cycle is normal, also things such as ill health or stress can delay your menstrual cycles too.
Irregular menstrual cycles mean that there is no predictability in a persons menstrual cycles. Typically when a person has irregular cycles there are weeks or months difference between menstruation and/or they may have irregular bleeds between menstruation. You an have monthly periods with an irregular cycle, but often people think their cycles are irregular because they don't understand that a persons cycles may not always be 28 days or that cycle lengths can change.
No. Humans are the only mammals with menstrual cycles. Deer, as well as other mammals, have estrous cycles. http://en.wikipedia.org/wiki/Estrous_cycle