Hi, I Had Unprotected Sex About A Month Ago And

Hi, I had unprotected sex about a month ago and after that I had dark brown discharge instead of bleeding that occurred for 4 days. Now, my recent period was also dark brown and lasted 4 days. Is this implantation bleeding? I am also on lo lestrinfe but I have previously had red period blood while I was on the pill. I am still taking the birth control. And I pregnant? Please help