Hi, I Had My Period Two Weeks Ago, And Now

Hi, I had my period two weeks ago, and now I am experiencing brown/pink discharge. I have never experienced this before, so this is quite alarming to me. The brown discharge has occurred the two times my significant other and I had sex. I am on birth control and we use protection everytime we have sex. I was recently prescribed sertraline 50mg (about 2 months ago).