I had my period on the 15th of this month until the 18th. On the 19th & 20th I had unprotected sex and my boyfriend finished in me. The next day the same thing happened and then we bought the Plan-B pill. On the 25th i saw a little brown spot on my undies. Then every time I would use the washroom when I would wipe myself a light brown came. However, the day after that it turned into bright red, so is today. Can this be implantation bleeding or can this be a result of taking the Plan-B pill?