Originally Posted by
WisperWill70
Yes it is normal for your period to start earlier than normal or a little later than normal by a few days. Menstruation can even become slightly irregular due to certain physical conditions. A period doesn't go by the calendar but an approximate 28 day cycle. However, even if you're regular like clockwork, your body may suddenly decide you're on a 21 day, or 34 days cycle and then switch back to your regular 28 days after a period of time... this is normal and OK. HOWEVER if you experience heavy period, missing periods or other physical symptoms more than being a little early or late... talk to your doctor.
Period irregularity can be caused by metabolic conditions, hormone changes and stress (as well as weight gain or loss).