Many reasons: There is a normal variation in cycle lenght so i would have to know what you consider "on time". It is unusual for periods to be the same day every month and 28 day cycles are an average but not all cycles will be 28 days. If they are very irregular you need to see a doctor to look into this.
Answered 4/29/2014
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A doctor has provided 1 answer
A doctor has provided 1 answer
A doctor has provided 1 answer
A doctor has provided 1 answer
A doctor has provided 1 answer
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