What's wrong with my period

My period which is usually reliable never missed one always consistent except this month. It was suppose to start Thursday nothing happen, Saturday however it came seemed normal . My period was normal Saturday and Sunday or so I thought . Monday was weird it was the 3rd day but it seemed as if it was ending barely any blood more of a brown color. My 3rd day is usually my heaviest I have had a consistent 5 day period from as long as I can remember . Today it's barely anything down there . It's defiantly a chance I could be pregnant .