Well 6 weeks ago i had unprotected sex a couple of days before my period was due. i have a 20-21 day cycle and my period is always heavy. this time it was 5 days late and lighter than usual. Now 2 weeks after its been off i have pink and brown spotting and a little cramping. but i've had 3 negative hpt....could i still be pregnant?? if not whats wrong with me??