For 3 months now every time me period comes it only lasts 3 days and its normally 5 days? Y is this? am I pregnant

There is no such thing as a normal period, even for a woman who has had a certain routine for a while. Our bodies change. Going from 5 days to 3 days means nothing. I started with 7 days of heavy periods and by the time I was 40 I was down to light spotting for 2 days.
You shouldn't be worrying about pregnancy because you should be using birth control - unless you want to be pregnant.