My period always comes two or three days before it's supposed to come, is this normal?

Cycle length. Most people's cycle length will be between 25 and 35 days from the start of one period to the next. Many people erroneously think it should start on the same date of each calendar month, but as you learned in 1st grade, not all months are the same length. If your cycle length is in the above range, you are normal.