Regular period?

Michelle • Hi I`m Michelle I`m 23 and have been off BC for 2 years now and still nothing yet!
I had my hormones tested in August and everything was normal I had a normal 4 day period. Then October I only had a 2 day period then November I only had a 2 day period. Is there any reasons why this is happening all of a sudden I have always had 4 day periods?