today, i've a blood stain on my panty.. i've had sex during my menstruation last march 14-16.. but my period came 2 days earlier then it only lasted for 3 days and it's my first to have it that way. then it stop for a day and i had my brown discharges for 5 days with associated cramps. then i had sex again last march 23 and today i had my spotting with a lower back pain and still on cramps around me but tolerable.. what this could be mean?