Darl brown spotting?

I have had so many pregnancy symptoms for weeks. Had spotting two days after sex well over a month ago. AF was due on the 13th of this month.. And now today I've had dark brown vaginal discharge/ spotting. Anyone have any ideas? The first say 3 wipes were pink/red then really dark red/brown colour. What could this be? Cramps and back pains, headaches and hot flushes are pretty unreal right this minute. Need advice.