What Causes Delay In Periods And Brownish Bleeding?

Am i pregnant?So on the 17th i had unprotected sex and my period was due 19th but it never came :/it was my first time and i bleeded something brownish and on the 19th i bleeded reaally red but just a lil when i went to the bathroom Also that week i drank almost daily so idk if that affects my period, also im not usually regular