Do Shorter, Light Periods And Brown Spotting Indicate Pregnancy?

Hi there I am 19 years old and I m having a major problem this month I had a short 2day period which was very light ( am not on anything and have been having unprotected sex) at the weekend I was out and a fight happened I tried to stop it and ended up getting kicked my 2 ribs belly then today I noticed I was spotting just a tiny bit of brown blood I m still sore ( my ribs) and I m worried what has this blood came for?