What Causes Delay In Periods And Pink Mucous Discharge?

I am always irregular... I have been having unprotected sex since Nov 2nd which was the last period I had... i am now 3 wks late... my breast are sore but more painful sore and today i saw some pink like mucousy discharge from my vagina... i was hoping it was my period but it is not...i feel cramping too... i took a pregnancy test 3 times and all came back negative... could i be pregnant??