Your period was only 3 days and it usually last 5 days could you be pregnant?

It is possible that you could be pregnant... if you are really concerned take a test.

If your period was very light for those 3 days, and mostly brown discharge and spotting instead of fresh blood I would be a lot more concerned. If you did actually have fresh blood or clotting during those 3 days than it is most likely you are not pregnant and your period was just a little different this month than normal.