Ive been having unprotected sex for about 3 weeks. My period is not very regular but was supposed to come on Jan 21 but it didn't now I have had a brown dishcharge for 3 days it wasn't heavy like a period but it wasn't just spotting either. Today is the third day it has happened and it's getting lighter. I need help , what could it be? Implantation or is my period beginning to start?