2 days periods

I took pregnancy test on 29th October 6:3am  which came negative and by afternoon started bleeding so i thought I am having my periods and m not pregnant, but the strange thing is that my periods lasted for 2 days only (usually it last for 4days) and bleeding on the day 1 was heavy and then lighter in 2nd day and spot on 3rd day.and 29th October is my usual cycle date.what could it be any suggestions any idea? Please say something instead of just visiting this question.😭