How come menstrual cycles come early ? I usually have mine like around 27th then as I notice it has been coming earlier and earlier.

Many different factors can change the cycle... I remember when I first moved in with a friend of mine, our periods came exactly at the same time... which was ealry for me and late for her. It can be all sorts of mental factors, or body factors, diets etc.

Could be due to stress, age, weight gain, weight loss... There are many variables to be able to pinpoint just one.