For 3 years my period started at the beginning of the month anywhere from the 1st-3rd without a fail. I could count on it to be the first of month never had irregular periods. Now for the last 10 months it s changed to starting on the 16-18th with out a fail no irregulars ever. Is that normal that my period would change a difference of 2 weeks and be regular for 10 months? FYI my period at the beginning of the year in jan. I m 28 years old and married no kids no birth control