What Causes Vaginal Bleeding After Sexual Intercourse?

Hello there I have a question I am on a birth control method that Igot in my arm & i had sexual intercourse with my partner about two be 2weeks ago & I just started feeling something pinch me in my stomach is it possible that I might be pregnant ? Although , i did start my mentrual but I m not sure if its from the birth control that I got can someone please answer my question !