Thanks for the query.
Some amount fluctuation in menstrual cycle is common.
You may not always have premenstrual symptoms.
And also 21+/-7 days length of the cycle can be taken as normal.
There could be minor alterations in the hormonal
levels which might have leading to these symptoms. No need to worry about them.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429