I used to have 6-7 days of periods before marriage but it has been reduced to 4-5 days after marriage with some spottings on the 5th day. I am married for 4 months now. I have noticed a gradual decrease in the number of days (from 6-7 days before marriage to 4-5 days now after 4 month). Can there be any reason for this?

Note: we do have sex during 4-5th day of the period when I don't notice anymore bleeding.