What Causes Spotting After Having Postinor 2?

hi doctor, would like to seek your advise, i had intercourse with my husband on 14th Feb, which is 2 weeks after my period commenced, i did not plan for pregnancy and due to unprotected sex i took a emergency contraceptive pill postinor 2 which i took it quite late. after 12 days approximately i felt my nipple soreness and breast tenderness and again 1 day later i started to sport some faint blood discharge when i wipe with tissue only, and it stopped yesterday, and my menses is delayed for almost 9 days now, i have also check with pregnancy test kit and had a negative result, im not sure if im pregnant, need your advise please