A little bit concerned

Ok so I have a question that you ladies may be able to answer. I am 25 and has a 6 year old. I started my period when I was 15. From the time I started up until 3 months ago, my periods have always been 5 days long. They've only been 1-2 days long. I have called my dr and she said as we age, our periods become shorter and before anyone says I'm pregnant, I've taken tests and they've all came out negative. I am not on BC and me and my boyfriend use the pull out method. I know it's not smart but we both hate condoms. Would anyone have any insight on what could be happening? Thanks in advance!!