My period is 3 days late and i'm experiencing watery discharge. what could this mean?

Start with test: If your period is late and you have been having unprotected intercourse, the first thing to do is a pregnancy test and, repeat it in 3-5 days if it is negative and your period still hasn't started. This could be nothing more than the normal variation in menstrual cycles with the discharge due to a vaginal infection. See someone if the second test is still negative. Best wishes. Hope this helps.