Had my period 3 weeks ago and bleeding again why it has never happend before..a?

Hormone change?: A woman's period will come 2 weeks after ovulation occurs, if ovulation does not occur, the period will be unpredictable and may come early or late. Ovulation may not occur for different reasons such as, pregnancy, stress, other hormone issues, weight changes, etc. If this becomes a pattern, please see your doctor to discuss further.