Rule out early pregnancy
Thanks for the query. Bleeding and unprotected sex bring the issue of a possible early pregnancy. 3 weeks after the date of unprotected sex, if there was conception, the pregnancy hormone should be able to be detected in blood or urine; that could be an option about how to proceed.
Sometimes, there are very early miscarriages that present as a "unusually light" period, and pregnancy needs to be ruled out.