There can be several causes behind your menses lasting for a shorter duration than normal. An average woman's periods usually last between 3 to 7 days.
The underlying causes generally will depend on a few factors for example:
A woman's age - whether the woman is approaching menopause
Any other underlying medical problems (e.g. thyroid issues)
Any other medications (e.g. birth control pills)
Lifestyle (e.g. stress or over strenuous exercise)
There can be many reasons behind a sudden change in your period - but if this is a sudden change that you noticed, i would recommend consulting a doctor to do some basic checks to rule out any underlying problems such as hormonal issues.
Best Regards,
Dr Michelle Chia