What Causes Spotting Without Bleeding During Periods?

hi, i started taken bromergon tablet 2.5mg prescribe by my doctor on 27th nov.2010. i was on it when my mensturation came out on the 20th of dec., there was a spot of blood. it was not flowing. there was no flow through out the four days. though i met my husband on d 9th day of my previous cycle. does it mean that i'm pregnant cos i was some related symptoms.