What Causes Brown Spotting After Taking Unwanted72?

Hello, I had my periods from Feb 6 to 10. I had unprotected sex on early morning on Feb 13, Feb 13 night, and 15. I took Unwanted 72 on Feb 14 evening. I see brown blood discharge today on Feb 19 morning. I want to know what this means, and if this could be a sign of pregnancy. Thanks.