Hallow Dear,
It seems, there is a minor variation in the regularity of your menstrual cycle; though variation by about 4 days plus or minus would not be considered as irregularity in the menses.
It is not clear from your history, for how many days your menses are postponed.
However, if you are not on any
contraceptive protection and you are sexually active, any delay in periods should be considered due to
pregnancy unless and until proved otherwise. To sort out the matter, you may opt one or all of the following:
1. Perform pregnancy test on overnight morning first urine sample about a week after the missed period; earlier the test may report false negative.
2. Alternatively you may opt for the
Beta hCG test on your blood anytime 10 days after the last unprotected sexual relation.
I am sure, this should resolve your dilemma.
Dr. Nishikant Shrotri